ex_menu context menu only works once on Linux.

[SiegeLord]

Steps to reproduce:

1. Open up ex_menu
2. Right click
3. Click away from the menu
4. Right click again

Currently at step (4) nothing happens, and there's log spam:

(ex_menu:9467): Gtk-WARNING **: 00:05:17.516: no trigger event for menu popup
Couldn't popup menu!