Changes

#673: Fix Craftworld#isChunkLoaded

The flag for getChunkAt(int, int, ChunkStatus, boolean)
is actually a flag for whether to bring the underlying
PlayerChunk up to the required ticket level to load the
chunk. So, if the chunk is already at the required level,
but has not yet loaded, the call will actually either
start the load if it has not already been started and
block until completion.

This behaviour is not suitable for just
checking if the chunk is loaded.