Don't try to get back() of empty vector in LootManager

Fixes #1207
Merge pull request #1208 from dorkster/fixes

Don't try to get back() of empty vector in LootManager
Fix clip rect for MenuEnemy background graphics

Noticed this bug with the SDL 2 hardware renderer, where the graphics
appeared to be stretched.
Merge pull request #1209 from dorkster/fixes

Fix clip rect for MenuEnemy background graphics