NullPointerException fix

Added != null when player walks throughthe teleporter.
Merge branch 'master' of github.com:DylanMeeus/JavaGame into DylanMeeus-master
Merge branch 'DylanMeeus-master' into bugfix-#5
Fixed NullPointerException for returing to world
Fixed a bug where the game crashes when you pressed Z without spwaning a dummy NPC
Merge branch 'bugfix-#5'