Bad error checking when building

[rycoll]

Currently, you can build a room with non-contiguous tiles, as long as each tile has a neighbour.
Additionally, I got some weird errors when building and playing: every set of tiles I tried to build came up with the non-contiguous error message.

[rycoll]

In addition to some somewhat negligent error checking, there is a null pointer exception that occurs in 'built' versions of the game, when setting neighbours of each MapTile.

Edit: the exception error has been fixed