Fixes rare crash on base facility dismantle

Deleting a base facility at x=2 y=3, so roughly where the ok button is
in the confirm deletion box, can occasionally cause a viewMouseOver
event to fire where the facility just was.

Marks the facility as being dismantled
Merge branch 'master' of https://github.com/SupSuper/OpenXcom into basescape_crash
Mark facility for dismantlement after user okays it
Reset selected facility when user dismantles

To avoid mouseover bugs on facility dismantlement, reset the selected
facility and remove it from our stored view.
missed those
already know coordinates
Merge pull request #493 from cfailde/basescape_crash

Fixes rare crash on base facility dismantle