cap max queued tiles

[nzjrs]

Yeah, I have had this before, where it goes and calculates a million
tiles to download if you try and cache the whole world at all zoom
levels.

What do you think a sensible sanity check would be?

what about capping the max-zoom-level at a value where the bounding box contains at most
128 tiles in either dimension? Would cap the queue to 16384 for a perfectly square
bounding box (still quite a lot), and it matches the max 7 zoom levels download of
foxtrotgps.