maxZIndex becomes NULL when the last feature is removed, p=pvalsecc, r=me (closes #1670)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@7712 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Renderer/Elements.js

@@ -128,24 +128,37 @@ OpenLayers.ElementsIndexer = OpenLayers.Class({
             
             // Reset the maxium z-index based on the last item in the 
             // order array.
-            var lastId = this.order[this.order.length - 1];
-            this.maxZIndex = this.indices[lastId];
+            if (this.order.length > 0) {
+                var lastId = this.order[this.order.length - 1];
+                this.maxZIndex = this.indices[lastId];
+            } else {
+                this.maxZIndex = 0;
+            }
         }
     },
     
+    /**
+     * APIMethod: clear
+     */
+    clear: function() {
+        this.order = [];
+        this.indices = {};
+        this.maxZIndex = 0;
+    },
+    
     /**
      * APIMethod: exists
-     * 
+     *
      * Parameters:
      * node- {DOMElement} The node to test for existence.
-     * 
+     *
      * Returns:
      * {Boolean} Whether or not the node exists in the indexer?
      */
     exists: function(node) {
         return (this.indices[node.id] != null);
     },
-    
+
     /**
      * APIMethod: getZIndex
      * Get the z-index value for the current node from the node data itself.
@@ -395,6 +408,7 @@ OpenLayers.Renderer.Elements = OpenLayers.Class(OpenLayers.Renderer, {
                 this.root.removeChild(this.root.firstChild);
             }
         }
+        this.indexer.clear();
     },
 
     /**