[Bug Fix] Fix segfaults related to world factory

Fixes segfault on exit that occurs due to MAPBUFFER.save_if_dirty() being called w/o an active_world being available. Ref issue #3988

Fix segfault on answering No in New Game > World Create query. Removed query since it only shows up if there are 0 worlds available and it should just automatically put the player to the world create screen anyway in that case. Ref issue #3979