Fix for issue #529.

* replaced precondition with if-statement in class ChunkMeshInfo.
Merge branch 'develop' into monitoring
Merge branch 'develop' of https://github.com/MovingBlocks/Terasology into monitoring
Merge #530 by @mbrotz to fix #529
Added DoubleClickListener to module dialog.
 Double clicking toggles mod selection.
fixed core mod toggle bug.