Fix 'Dereference of null pointer' from scan-build-10

These are mostly false positives, the clang-analyzer FAQ[1] specifies
why and how to fix it:

> The reason the analyzer often thinks that a pointer can be null is
> because the preceding code checked compared it against null. So if you
> are absolutely sure that it cannot be null, remove the preceding check
> and, preferably, add an assertion as well.

The 2 warnings reported are:

byname_test.c:308:34: warning: Access to field 'fwdtable' results in a dereference of a null pointer (loaded from variable 'view')
                RUNTIME_CHECK(dns_fwdtable_add(view->fwdtable, dns_rootname,
                                               ^~~~~~~~~~~~~~
/builds/isc-projects/bind9/lib/isc/include/isc/util.h:318:52: note: expanded from macro 'RUNTIME_CHECK'
                                                   ^~~~
/builds/isc-projects/bind9/lib/isc/include/isc/error.h:50:21: note: expanded from macro 'ISC_ERROR_RUNTIMECHECK'
        ((void)(ISC_LIKELY(cond) ||  \
                           ^~~~
/builds/isc-projects/bind9/lib/isc/include/isc/likely.h:23:43: note: expanded from macro 'ISC_LIKELY'
                                            ^
1 warning generated.

--

./rndc.c:255:6: warning: Dereference of null pointer (loaded from variable 'host')
        if (*host == '/') {
            ^~~~~
1 warning generated.

References:
1. https://clang-analyzer.llvm.org/faq.html#null_pointer

(cherry picked from commit ddd0d356)
(cherry picked from commit 9b76eea0)
63 jobs for !3290 with ondrej/scan-build-10-fixes-v9_11-v9_14 in 22 minutes and 59 seconds (queued for 5 minutes and 12 seconds)
detached
Status Job ID Name Coverage
  Precheck
passed #783506
amd64 linux
🐞:sid:amd64

00:00:59

passed #783504
amd64 linux
autoreconf:sid:amd64

00:00:36

failed #783505
amd64 linux
misc:sid:amd64

00:00:30

 
  Build
passed #783520
amd64 linux
asan:sid:amd64

00:04:16

passed #783524
amd64 libvirt
clang:freebsd11.3:amd64

00:01:46

passed #783525
amd64 libvirt
clang:freebsd12.1:amd64

00:01:52

passed #783526
amd64 libvirt
clang:openbsd6.6:amd64

00:04:44

failed #783521
amd64 linux
clang:stretch:amd64

00:00:29

failed #783522
i386 linux
clang:stretch:i386

00:00:52

passed #783507
amd64 linux
gcc:alpine3.11:amd64

00:02:38

passed #783519
amd64 linux
gcc:bionic:amd64

00:02:33

passed #783512
amd64 linux
gcc:buster:amd64

00:02:15

passed #783508
amd64 linux
gcc:centos6:amd64

00:02:13

passed #783509
amd64 linux
gcc:centos7:amd64

00:02:22

passed #783510
amd64 linux
gcc:centos8:amd64

00:01:57

passed #783517
amd64 linux
gcc:fedora31:amd64

00:02:21

passed #783513
amd64 linux
gcc:sid:amd64

00:04:31

passed #783515
i386 linux
gcc:sid:i386

00:03:09

passed #783511
amd64 linux
gcc:stretch:amd64

00:03:08

passed #783516
amd64 linux
gcc:tumbleweed:amd64

00:02:28

passed #783518
amd64 linux
gcc:xenial:amd64

00:02:40

passed #783528
amd64 windows
msvc:windows:amd64

00:02:31

passed #783527
amd64 linux
nolibtool:sid:amd64

00:02:48

passed #783514
amd64 linux
oot:sid:amd64

00:03:22

passed #783523
amd64 linux
pkcs11:sid:amd64

00:02:25

 
  Unit
passed #783541
amd64 linux
unit:asan:sid:amd64

00:00:40

passed #783544
amd64 libvirt
unit:clang:freebsd11.3:amd64

00:00:50

passed #783545
amd64 libvirt
unit:clang:freebsd12.1:amd64

00:00:52

skipped #783542
amd64 linux
unit:clang:stretch:amd64
passed #783529
amd64 linux
unit:gcc:alpine3.11:amd64

00:00:41

passed #783540
amd64 linux
unit:gcc:bionic:amd64

00:00:46

passed #783534
amd64 linux
unit:gcc:buster:amd64

00:00:53

passed #783530
amd64 linux
unit:gcc:centos6:amd64

00:00:51

passed #783531
amd64 linux
unit:gcc:centos7:amd64

00:00:53

passed #783532
amd64 linux
unit:gcc:centos8:amd64

00:00:51

passed #783538
amd64 linux
unit:gcc:fedora31:amd64

00:00:49

passed #783535
amd64 linux
unit:gcc:sid:amd64

00:00:49

passed #783536
i386 linux
unit:gcc:sid:i386

00:00:49

passed #783533
amd64 linux
unit:gcc:stretch:amd64

00:00:35

passed #783537
amd64 linux
unit:gcc:tumbleweed:amd64

00:00:50

passed #783539
amd64 linux
unit:gcc:xenial:amd64

00:00:53

passed #783546
amd64 linux
unit:nolibtool:sid:amd64

00:01:09

failed #783543
amd64 linux
unit:pkcs11:sid:amd64

00:01:08

 
  System
failed #783559
amd64 linux
system:asan:sid:amd64

00:13:47

passed #783561
amd64 libvirt
system:clang:freebsd11.3:amd64

00:10:23

passed #783562
amd64 libvirt
system:clang:freebsd12.1:amd64

00:11:06

passed #783547
amd64 linux
system:gcc:alpine3.11:amd64

00:11:40

passed #783558
amd64 linux
system:gcc:bionic:amd64

00:10:57

passed #783552
amd64 linux
system:gcc:buster:amd64

00:11:08

passed #783548
amd64 linux
system:gcc:centos6:amd64

00:10:24

failed #783549
amd64 linux
system:gcc:centos7:amd64

00:13:03

passed #783550
amd64 linux
system:gcc:centos8:amd64

00:10:32

passed #783556
amd64 linux
system:gcc:fedora31:amd64

00:11:18

passed #783553
amd64 linux
system:gcc:sid:amd64

00:10:54

passed #783554
i386 linux
system:gcc:sid:i386

00:11:06

passed #783551
amd64 linux
system:gcc:stretch:amd64

00:10:58

passed #783555
amd64 linux
system:gcc:tumbleweed:amd64

00:10:17

passed #783557
amd64 linux
system:gcc:xenial:amd64

00:10:47

passed #783563
amd64 linux
system:nolibtool:sid:amd64

00:11:17

failed #783560
amd64 linux
system:pkcs11:sid:amd64

00:08:03

 
  Docs
passed #783564
amd64 linux
docs:sid:amd64

00:01:02

 
  Postcheck
failed #783566
amd64 linux
cppcheck:gcc:sid:amd64

00:00:22

failed #783565
amd64 linux
scan-build:buster:amd64

00:00:29

 
Name Stage Failure
failed
system:asan:sid:amd64 System
No job log
failed
system:gcc:centos7:amd64 System
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system:pkcs11:sid:amd64 System
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failed
cppcheck:gcc:sid:amd64 Postcheck
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unit:pkcs11:sid:amd64 Unit
No job log
failed
scan-build:buster:amd64 Postcheck
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clang:stretch:i386 Build
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failed
clang:stretch:amd64 Build
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failed
misc:sid:amd64 Precheck
No job log