DRAFT: SIGSEGV|bg_slave_kill|handle_manager|start_thread|clone3

Pquery found this sporadic crash on the debug build which is difficult to reproduce locally.

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Core was generated by `/test/MDEV-32570-MD220126-mariadb-12.3.0-linux-x86_64-dbg/bin/mariadbd --no-def'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x00005c4f04ecc625 in bg_slave_kill (victim=0x127330000d58) at /test/main-MDEV-32570-preview_dbg/sql/slave.cc:498
498 to_kill->rgi_slave->killed_for_retry= rpl_group_info::RETRY_KILL_KILLED;
[Current thread is 1 (LWP 3438588)]
(gdb) bt
#0 0x00005c4f04ecc625 in bg_slave_kill (victim=0x127330000d58) at /test/main-MDEV-32570-preview_dbg/sql/slave.cc:498
#1 0x00005c4f050037dd in handle_manager (arg=0x0) at /test/main-MDEV-32570-preview_dbg/sql/sql_manager.cc:120
#2 0x00001273bb49caa4 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:447
#3 0x00001273bb529c6c in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78
(gdb)

Preliminary analysis:
The crash has happened only on the debug build.
It's a slave crash.
From the bulk sql file which caused the crash, it seems a SHUTDOWN command has caused the above crash.