Fix up crashes removing the MarkerClusterGroup from the map in a zoomstart/end handler. Crashes could come still happen depending on the order the handlers were called. Refs #36

src/MarkerCluster.Spiderfier.js

@@ -320,12 +320,17 @@ L.MarkerClusterGroup.include({
 	_spiderfierOnRemove: function () {
 		this._map.off('click', this._unspiderfyWrapper, this);
 		this._map.off('zoomstart', this._unspiderfyZoomStart, this);
+		this._map.off('zoomanim', this._unspiderfyZoomAnim, this);
 	},
 
 
 	//On zoom start we add a zoomanim handler so that we are guaranteed to be last (after markers are animated)
 	//This means we can define the animation they do rather than Markers doing an animation to their actual location
 	_unspiderfyZoomStart: function () {
+		if (!this._map) { //May have been removed from the map by a zoomEnd handler
+			return;
+		}
+
 		this._map.on('zoomanim', this._unspiderfyZoomAnim, this);
 	},
 	_unspiderfyZoomAnim: function (zoomDetails) {

src/MarkerClusterGroup.js

@@ -222,7 +222,9 @@ L.MarkerClusterGroup = L.FeatureGroup.extend({
 	},
 
 	_zoomEnd: function () {
-
+		if (!this._map) { //May have been removed from the map by a zoomEnd handler
+			return;
+		}
 		this._mergeSplitClusters();
 
 		this._zoom = this._map._zoom;