TileEntityChestRenderer bugfix patch

Fixed an unchecked cast to BlockChest that could sometimes cause a
crash.

I kept experiencing this crash during generating structures in my mod, so I submitted this patch to fix it.

I believe the crash is caused by the renderer trying to render a chest when the world has not yet updated the blocks, and it attempts to cast an unrelated block (which should be a chest, but has not updated yet) to BlockChest.