Spigot made structure start not load chunks, but forgot to null check
the result...
This likely never blew up before due to the chunk leak issue, but now
that leaky chunks are cleaned up, it was identified.
While last was mostly there, still had some slight risk of unloading
before it was fully finished.
So just going to bump the delay to 3 minutes to be safe. Better than
forever at least.
Was really hoping we could unload them as soon as they were done to
any memory prematurely promoting to old generation, but guess we can't.
A chunk was loaded but not yet finished in use and was unloaded too early.
This caused it to be reloaded again or caused crashes.
Now also check if the chunk pops out of the unload queue that it also
doesn't now have a ticket either.
Due to some complexity in mojangs complicated chain of juggling
whether or not a chunk should be unloaded when the last ticket is
removed, many chunks are remaining around in the cache.
These chunks are never being targetted for unload because they are
vastly out of view distance range and have no reason to be looked at.
This is a huge issue for performance because we have to iterate these
chunks EVERY TICK... This is what's been leading to high SELF time in
Ticking Chunks timings/profiler results.
We will now detect these chunks in that iteration, and automatically
add it to the unload queue when the chunk is found without any tickets.
Aikar