Commit
58bff62b2dc68da958f2e90371582a13aa3c9355
by md_5SPIGOT-2891: Remove chunks if first check is false
Minecraft does double checking for synchronous generation, but since we
generate chunks asynchronously we are required to check the first
condition also in case the chunk was loaded between ticks. We leave the
other logic to be cleaned up by the loops below.