Comment 13 for bug 1964777

With debuginfo into libspice this looks like:

(gdb) bt
#0 __pthread_create_2_1 (newthread=0x5555572d4f10, attr=0x0, start_routine=0x7ffff7e33950 <red_worker_main(void*)>, arg=0x5555572d4f10) at ./nptl/pthread_create.c:621
#1 0x00007ffff7eb11e6 in red_worker_run.isra.0 (worker=worker@entry=0x5555572d4f10) at ../server/red-worker.cpp:1127
#2 0x00007ffff7e2c4eb in red_qxl_init (qxl=0x555557194c08, reds=<optimized out>) at ../server/red-qxl.cpp:583
#3 spice_server_add_interface(SpiceServer*, SpiceBaseInstance*) (reds=<optimized out>, sin=0x555557194c08) at ../server/reds.cpp:3248
#4 0x0000555555a8c078 in qemu_spice_add_interface (sin=0x555557194c08) at ../ui/spice-core.c:874
#5 0x0000555555a8c2d1 in qemu_spice_add_display_interface (qxlin=0x555557194c08, con=0x555557133c00) at ../ui/spice-core.c:944

Now that we know that much this changelog entry in spice is suspicious
  "Fix some potential thread race condition in RedClient"
But none of the commits was immediately obvious as being "the one"

Gladly I can reproduce this from spice git and spice builds fast,
so we can bisect spice to be sure what change it was without making
too many assumptions.