Find out why vtile.getTile returns "Tile does not exist" #126
Description
#125 adds the EMAPNIK eror code within the source.profile() method so that errors can be handled properly in mapbox-upload validate (refs https://github.com/mapbox/mapbox-upload-validate/blob/master/lib/validators/tm2z.js#L19).
NOTE: I think this is a stopgap to a deeper mapnik bug. The style added here was valid in mapnik 3.4.17, but invalid in 3.5.6 because of a Tile does not exist error. This smells like something else is afoot, and while that PR fixes the missing code and should be merged, we should solve the underlying issue asap.