Mapbox "empty" tile

[Bernhard Hiller <bhil@…>]

If tiles are not available at high zoom level, Mapbox sends some kind of "empty" tile, i.e. a black tile with a grey cross in it:

Instead of a "no tiles at this zoom level" message and stretching of lower zoom tiles, JOSM shows those empty tiles.
This behavior can be seen e.g. in the Perlis region of Malaysia: maximum zoom level available is 17.
It seems that the machanism for detecting the maximum zoom level does not work with Mapbox. What about using the file size of the tile, followed by an MD5 checksum test to determine if a tile is such an empty tile or not?

[Bernhard Hiller <bhil@…>]

See also ticket #10451