Comment 12 for bug 1964777

With the old lib, when the `qemu_spice_display_start` happens in the main
thread the spawned "SPICE worker" still is at:

(gdb) bt
#0 0x00007ffff770ad7f in __GI___poll (fds=0x7fffb80031b0, nfds=2, timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
#1 0x00007ffff7ab6686 in () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007ffff7a61293 in g_main_loop_run () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ffff7e311ca in () at /lib/x86_64-linux-gnu/libspice-server.so.1
#4 0x00007ffff7686b43 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#5 0x00007ffff7718a00 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

That means it is pretty much still waiting at spawn-time.

But the TL;DR so far is:
- affects different qemu versions
- some change in spice causes it
- this clearly is a race
- the display initializes later and from there things are ok
- being a race in general explains why I've found it in various unrelated logs

TODO: find why it seems to be happen consistently in Jammy with the new spice version