Assign fctx->client when fctx is created rather when the join happens.

This prevents races on fctx->client whenever a new fetch joins a existing
fetch (by calling fctx_join) as it is now invariant for the active life of
fctx.

(cherry picked from commit 9ca6ad63)
69 jobs for !2695 with 1416-threadsanitizer-data-race-resolver-c-3384-in-findname-v9_11 in 19 minutes and 36 seconds (queued for 5 seconds)
latest detached
Status Job ID Name Coverage
  Precheck
passed #448935
amd64 linux
🐞:sid:amd64

00:01:07

passed #448933
amd64 linux
autoreconf:sid:amd64

00:00:33

passed #448934
amd64 linux
misc:sid:amd64

00:00:18

 
  Build
passed #448948
amd64 linux
asan:sid:amd64

00:02:13

passed #448953
amd64 freebsd
clang:freebsd11.3:amd64

00:01:27

passed #448954
amd64 freebsd
clang:freebsd12.0:amd64

00:01:13

passed #448955
amd64 openbsd
clang:openbsd6.5:amd64

00:06:25

passed #448949
amd64 linux
clang:stretch:amd64

00:01:45

passed #448950
i386 linux
clang:stretch:i386

00:01:41

passed #448936
amd64 linux
gcc:alpine3.10:amd64

00:02:44

passed #448947
amd64 linux
gcc:bionic:amd64

00:01:33

passed #448942
amd64 linux
gcc:buster:amd64

00:03:03

passed #448937
amd64 linux
gcc:centos6:amd64

00:01:40

passed #448938
amd64 linux
gcc:centos7:amd64

00:02:37

passed #448939
amd64 linux
gcc:centos8:amd64

00:02:04

passed #448945
amd64 linux
gcc:fedora30:amd64

00:02:31

passed #448940
amd64 linux
gcc:jessie:amd64

00:01:46

passed #448943
amd64 linux
gcc:sid:amd64

00:04:00

passed #448944
i386 linux
gcc:sid:i386

00:01:25

passed #448941
amd64 linux
gcc:stretch:amd64

00:02:04

passed #448946
amd64 linux
gcc:xenial:amd64

00:01:38

passed #448957
amd64 windows
msvc:windows:amd64

00:02:25

passed #448951
amd64 linux
nocrypto:sid:amd64

00:01:19

passed #448956
amd64 linux
nolibtool:sid:amd64

00:02:11

passed #448952
amd64 linux
pkcs11:sid:amd64

00:01:31

 
  Unit
passed #448970
amd64 linux
unit:asan:sid:amd64

00:01:47

passed #448974
amd64 freebsd
unit:clang:freebsd11.3:amd64

00:00:34

passed #448975
amd64 freebsd
unit:clang:freebsd12.0:amd64

00:00:22

passed #448971
amd64 linux
unit:clang:stretch:amd64

00:00:45

passed #448958
amd64 linux
unit:gcc:alpine3.10:amd64

00:00:53

passed #448969
amd64 linux
unit:gcc:bionic:amd64

00:00:49

passed #448964
amd64 linux
unit:gcc:buster:amd64

00:00:54

passed #448959
amd64 linux
unit:gcc:centos6:amd64

00:00:56

passed #448960
amd64 linux
unit:gcc:centos7:amd64

00:00:55

passed #448961
amd64 linux
unit:gcc:centos8:amd64

00:00:55

passed #448967
amd64 linux
unit:gcc:fedora30:amd64

00:00:56

passed #448962
amd64 linux
unit:gcc:jessie:amd64

00:00:28

passed #448965
amd64 linux
unit:gcc:sid:amd64

00:00:46

passed #448966
i386 linux
unit:gcc:sid:i386

00:00:44

passed #448963
amd64 linux
unit:gcc:stretch:amd64

00:00:53

passed #448968
amd64 linux
unit:gcc:xenial:amd64

00:00:46

passed #448972
amd64 linux
unit:nocrypto:sid:amd64

00:00:53

passed #448976
amd64 linux
unit:nolibtool:sid:amd64

00:01:29

passed #448973
amd64 linux
unit:pkcs11:sid:amd64

00:00:58

 
  System
passed #448989
amd64 linux
system:asan:sid:amd64

00:06:56

passed #448992
amd64 freebsd
system:clang:freebsd11.3:amd64

00:05:09

passed #448993
amd64 freebsd
system:clang:freebsd12.0:amd64

00:04:59

passed #448977
amd64 linux
system:gcc:alpine3.10:amd64

00:06:04

passed #449130
linux amd64
system:gcc:bionic:amd64

00:05:02

passed #448983
amd64 linux
system:gcc:buster:amd64

00:05:26

passed #448978
amd64 linux
system:gcc:centos6:amd64

00:05:18

passed #448979
amd64 linux
system:gcc:centos7:amd64

00:05:14

passed #448980
amd64 linux
system:gcc:centos8:amd64

00:05:35

passed #449135
linux amd64
system:gcc:fedora30:amd64

00:05:23

passed #448981
amd64 linux
system:gcc:jessie:amd64

00:05:25

passed #448984
amd64 linux
system:gcc:sid:amd64

00:05:27

passed #448985
i386 linux
system:gcc:sid:i386

00:05:26

passed #448982
amd64 linux
system:gcc:stretch:amd64

00:05:01

passed #449131
linux amd64
system:gcc:xenial:amd64

00:05:20

passed #448990
amd64 linux
system:nocrypto:sid:amd64

00:03:06

passed #449136
linux amd64
system:nolibtool:sid:amd64

00:05:27

passed #448991
amd64 linux
system:pkcs11:sid:amd64

00:05:25

failed #448988
amd64 linux
system:gcc:bionic:amd64

00:05:18

failed #448986
amd64 linux
system:gcc:fedora30:amd64

00:05:44

failed #448987
amd64 linux
system:gcc:xenial:amd64

00:05:36

failed #448994
amd64 linux
system:nolibtool:sid:amd64

00:06:17

 
  Docs
passed #448995
amd64 linux
docs:sid:amd64

00:00:58

 
  Postcheck
passed #448997
amd64 linux
cppcheck:gcc:sid:amd64

00:01:28

passed #448996
amd64 linux
scan-build:buster:amd64

00:12:15