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
Merge pull request #1325 from dorkster/fixes

Prevent input during game load; Don't save invalid respawn points