GSocket – GSocketSource finalizing not threadsafe on Windows

The requested_conditions list access is not threadsafe. When passing
the socket ownership from a GSource callback to another thread, which
also creates a GSocketSource for the socket, it can happen that the
original GSocketSource is finalized at the same time as the new one
is created. This would cause inconsistencies in the requested_conditions
list and can cause assertions or completely undefined behaviour.

https://bugzilla.gnome.org/show_bug.cgi?id=705027