BUGFIX: Adjust zoom handling for cluster marker

Always zoom in when you click the cluster marker. If zoomOnClick is enabled and the map aspect ration
is special the zoom in does not work.

See issue googlemaps#437 for more information.

markerclustererplus/src/markerclusterer.js

@@ -149,6 +149,7 @@ ClusterIcon.prototype.onAdd = function () {
     if (!cDraggingMapByCluster) {
       var theBounds;
       var mz;
+      var currentZoom;
       var mc = cClusterIcon.cluster_.getMarkerClusterer();
       /**
        * This event is fired when a cluster marker is clicked.
@@ -161,20 +162,23 @@ ClusterIcon.prototype.onAdd = function () {
 
       // The default click handler follows. Disable it by setting
       // the zoomOnClick property to false.
+      // CORE-PATCH begin by Markus Günther
+      // For more details look at the github issue https://github.com/googlemaps/v3-utility-library/issues/437
       if (mc.getZoomOnClick()) {
         // Zoom into the cluster.
         mz = mc.getMaxZoom();
+        currentZoom = mc.getMap().getZoom();
         theBounds = cClusterIcon.cluster_.getBounds();
+
         mc.getMap().fitBounds(theBounds);
         // There is a fix for Issue 170 here:
         setTimeout(function () {
+          var newZoom = (mz !== null && (currentZoom > mz) ? mz : currentZoom) + 1;
           mc.getMap().fitBounds(theBounds);
-          // Don't zoom beyond the max zoom level
-          if (mz !== null && (mc.getMap().getZoom() > mz)) {
-            mc.getMap().setZoom(mz + 1);
-          }
+          mc.getMap().setZoom(newZoom);
         }, 100);
       }
+      // CORE-PATCH end by Markus Günther
 
       // Prevent event propagation to the map:
       e.cancelBubble = true;