bug#41239: GTK builds crashing in XTread_socket after deleting a frame

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Cc: martin rudalics <rudalics@gmx.at>,  41239@debbugs.gnu.org
> Date: Tue, 19 May 2020 21:50:35 -0400
> 
> > Once again, all the crashes are inside memory-allocation functions,
> > which suggests some kind of memory corruption.  Did someone try to run
> > this scenario under valgrind?
> 
> I've tried it now, log attached (minus what I believe are some false
> positives that printed during startup).  This is against latest master

Thanks.  This seems to say that we cause some memory allocation in
functions called by xg_prepare_tooltip, but the allocated memory
region is not large enough, and that causes invalid reads beyond end
of allocated region when we call xg_free_frame_widgets (as side effect
of deleting the tooltip frame, I suppose).

Can someone spot where we pass some wrong parameters to GTK/GIO
functions in xg_prepare_tooltip?  Or something we do wrong in
xg_free_frame_widgets?  Failing that, I guess we will need to step
through the GTK functions mentioned by valgrind and see what's going
on there.