Single tileUrlFunction in createFromTileUrlFunctions

In that case, simply return the single tileUrlFunction.

src/ol/tileurlfunction.js

@@ -60,6 +60,9 @@ ol.TileUrlFunction.createFromTemplates = function(templates) {
  * @return {ol.TileUrlFunctionType} Tile URL function.
  */
 ol.TileUrlFunction.createFromTileUrlFunctions = function(tileUrlFunctions) {
+  if (tileUrlFunctions.length === 1) {
+    return tileUrlFunctions[0];
+  }
   return function(tileCoord, tileGrid, projection) {
     if (goog.isNull(tileCoord)) {
       return undefined;