If a menu was not attached to any widget, we try to calculate its
position given where the grabbed pointer is and what window has its
focus. Previously we failed to do so if a "transfer window" was used
for the grab, and this patch adds a code path that, if the menu window
itself didn't have the grab, look for the transfer window and get the
grab device from there.
https://bugzilla.gnome.org/show_bug.cgi?id=748951
85635457bc