If a scene is modified and a user closes the editor and selects the "Save
and exit" option in the modal dialog -- the editor crashes. This appears
to be a result of the message queue being memdeleted AFTER visual servers
have been destroyed. Remnant textures handled by the message queue throw a
NRE when their own ~Texture destructors reference the visual servers.
This fixes bugs: #12946 and #12813.
0f223783dc
