virsh didn't call virInitialize(), which (among other things)
initializes virLastErr thread local variable. As a result of that, virsh
could just segfault in virEventRegisterDefaultImpl() since that is the
first call that touches (resets) virLastErr.

I have no idea what lucky coincidence made this bug visible but I was
able to reproduce it in 100% cases but only in one specific environment
which included building in sandbox.