Don't skip frames when game is paused

Closes #1321
Merge pull request #1326 from dorkster/frameskip

Don't skip frames when game is paused
Lock input when the player is in maps/spawn.txt

There was a brief moment when creating/loading a game where the player
could move while ignoring any map collision. This would cause the player
to be infinitely stuck on maps/spawn.txt. Locking input prevents this.
Don't have spawn position/map when it is an invalid tile