Return rather than fail if resolution is not defined
Merge pull request #2527 from pagameba/cluster-fix

Return rather than fail if resolution is not defined
Merge pull request #2539 from elemoine/tilecoord

Change ol.TileCoord to Array.<number>
Use opt_tileCoord in ol.source.WMTS tileUrlFunction
Use tmpExtent in ol.source.WMTS tileUrlFunction