Account for null or undefined geometry

The change in #2098 made it so a feature's geometry could be undefined.  This is consistent with the return type for the getGeometry method.  Where calling code needs to ensure that it has a geometry instance, it can use instanceof, goog.isDefAndNotNull(), or test for a truthy value.

src/ol/source/formatvectorsource.js

@@ -125,7 +125,7 @@ ol.source.FormatVector.prototype.readFeatures = function(source) {
       for (i = 0, ii = features.length; i < ii; ++i) {
         var feature = features[i];
         var geometry = feature.getGeometry();
-        if (!goog.isNull(geometry)) {
+        if (goog.isDefAndNotNull(geometry)) {
           geometry.applyTransform(transform);
         }
       }