dns_rbt_formatnodename() related crash in rpz system test

Job #2876768 failed for 169709af.

It might be a shutdown crash as the test starts with nextpart():

I:rpz:checking NSDNAME rewrites (5)
; Communication with 10.53.0.3#10223 failed: connection refused
could not reach any name server
I:rpz:failed; ns3 server crashed and restarted
I:rpz:wrong test3 ns3 statistics of 0 instead of 9

D:rpz:Core was generated by `/builds/isc-projects/bind9/bin/named/.libs/named -D rpz-ns3 -X named.lock -m re'.
D:rpz:Program terminated with signal SIGABRT, Aborted.
D:rpz:#0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
D:rpz:[Current thread is 1 (Thread 0x7f5e4fbfd640 (LWP 28428))]
D:rpz:#0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
D:rpz:#1  0x00007f5e821b15df in __pthread_kill_internal (signo=6, threadid=<optimized out>) at ./nptl/pthread_kill.c:78
D:rpz:#2  0x00007f5e82165a02 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
D:rpz:#3  0x00007f5e82150469 in __GI_abort () at ./stdlib/abort.c:79
D:rpz:#4  0x000055f82a579b7a in assertion_failed (file=<optimized out>, line=<optimized out>, type=<optimized out>, cond=0x7f5e82d6ebb0 "((node) != ((void *)0) && ((const isc__magic_t *)(node))->magic == ((('R') << 24 | ('B') << 16 | ('N') << 8 | ('O'))))") at main.c:238
D:rpz:#5  0x00007f5e82df2c1a in isc_assertion_failed (file=file@entry=0x7f5e82d6f4cc "rbt.c", line=line@entry=1478, type=type@entry=isc_assertiontype_require, cond=cond@entry=0x7f5e82d6ebb0 "((node) != ((void *)0) && ((const isc__magic_t *)(node))->magic == ((('R') << 24 | ('B') << 16 | ('N') << 8 | ('O'))))") at assertions.c:49
D:rpz:#6  0x00007f5e82c598ba in dns_rbt_formatnodename (node=node@entry=0x7f5e7000d9c0, printname=printname@entry=0x7f5e4fbfbbc0 "sub1.tld2.rpz-nsdname.bl", size=size@entry=1024) at rbt.c:1478
D:rpz:#7  0x00007f5e82c5d461 in delete_node (rbtdb=rbtdb@entry=0x7f5e700074e0, node=0x7f5e7000d9c0) at rbtdb.c:1867
D:rpz:#8  0x00007f5e82c65973 in decrement_reference (rbtdb=rbtdb@entry=0x7f5e700074e0, node=node@entry=0x7f5e7000d9c0, least_serial=<optimized out>, least_serial@entry=0, nlocktypep=nlocktypep@entry=0x7f5e4fbfc08c, tlocktypep=tlocktypep@entry=0x7f5e14002654, pruning=pruning@entry=false) at rbtdb.c:2214
D:rpz:#9  0x00007f5e82c65d4b in dereference_iter_node (rbtdbiter=rbtdbiter@entry=0x7f5e14002630) at rbtdb.c:9033
D:rpz:#10 0x00007f5e82c65f0e in dbiterator_next (iterator=0x7f5e14002630) at rbtdb.c:9407
D:rpz:#11 0x00007f5e82beb458 in dns_dbiterator_next (iterator=<optimized out>) at dbiterator.c:89
D:rpz:#12 0x00007f5e82cd281b in update_nodes (rpz=rpz@entry=0x55f82b5e7550, newnodes=<optimized out>) at rpz.c:1838
D:rpz:#13 0x00007f5e82cd398a in update_rpz_cb (data=0x55f82b5e7550) at rpz.c:1924
D:rpz:#14 0x00007f5e82e20366 in isc__work_cb (req=<optimized out>) at work.c:27
D:rpz:#15 0x00007f5e82615da5 in ?? () from /lib/x86_64-linux-gnu/libuv.so.1
D:rpz:#16 0x00007f5e821af84a in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
D:rpz:#17 0x00007f5e82232530 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:100
D:rpz:--------------------------------------------------------------------------------
D:rpz:full backtrace from rpz/ns3/core.28393 saved in rpz/ns3/core.28393-backtrace.txt
D:rpz:core dump rpz/ns3/core.28393 archived as rpz/ns3/core.28393.gz