Fix #7.   - World entities are set to null while they are loading.   - World's `loopOverEntities` doesn't loop over null (loading) entities.
Fix #7.
  - World entities are set to null while they are loading.
  - World's `loopOverEntities` doesn't loop over null (loading) entities.

ChaseMoskal/Nanoshooter,ChaseMoskal/Nanoshooter