Fixes #1006 the invisible UI object bug

This isn't a good fix, but the real fix would require massive changes to human/update_icons.dm. NOPE.avi. If you're feeling antsy, PM me.

To reproduce the problem every round, in mob.dm change update_icon = 1 to 0.
Merge pull request #2760 from MrPerson/invisible_cheeseburger

Fixes #1006 the invisible UI object bug