Resolved issue with cluster source reloading

The cluster source was not reloading when a map was panned, only when
the resolution changed.

src/ol/source/clustersource.js

@@ -77,10 +77,10 @@ ol.source.Cluster.prototype.getSource = function() {
  */
 ol.source.Cluster.prototype.loadFeatures = function(extent, resolution,
     projection) {
+  this.source_.loadFeatures(extent, resolution, projection);
   if (resolution !== this.resolution_) {
     this.clear();
     this.resolution_ = resolution;
-    this.source_.loadFeatures(extent, resolution, projection);
     this.cluster_();
     this.addFeatures(this.features_);
   }