Additional zoom levels don't work if maxNativeZoom is 0

[farowebshare]

If there is just one tile and maxNativeZoom is set to 0, the map goes blank in the additional zoom levels.

Reason: In _getTileSize and _getZoomForUrl the checks based on maxNativeZoom also return false if it is 0. Changing the check to something like (typeof zoomN === 'number') seems to have fixed the bug.

Version: 0.7.1. Verified that problem still exists in current develop version.

[mourner]

Hmm, what's the use case of having a TileLayer with one tile and maNativeZoom = 0 anyway?

[farowebshare]

The maps used in our web application are created automatically by a desktop software based on user-created projects. So a map with just a single tile is theoretically possible, at least for test projects.