fix($rootScope): allow destroying a root scope

src/ng/rootScope.js

@@ -861,22 +861,21 @@ function $RootScopeProvider() {
        * clean up DOM bindings before an element is removed from the DOM.
        */
       $destroy: function() {
-        // we can't destroy the root scope or a scope that has been already destroyed
+        // We can't destroy a scope that has been already destroyed.
         if (this.$$destroyed) return;
         var parent = this.$parent;
 
         this.$broadcast('$destroy');
         this.$$destroyed = true;
-        if (this === $rootScope) return;
 
         for (var eventName in this.$$listenerCount) {
           decrementListenerCount(this, this.$$listenerCount[eventName], eventName);
         }
 
         // sever all the references to parent scopes (after this cleanup, the current scope should
         // not be retained by any of our references and should be eligible for garbage collection)
-        if (parent.$$childHead == this) parent.$$childHead = this.$$nextSibling;
-        if (parent.$$childTail == this) parent.$$childTail = this.$$prevSibling;
+        if (parent && parent.$$childHead == this) parent.$$childHead = this.$$nextSibling;
+        if (parent && parent.$$childTail == this) parent.$$childTail = this.$$prevSibling;
         if (this.$$prevSibling) this.$$prevSibling.$$nextSibling = this.$$nextSibling;
         if (this.$$nextSibling) this.$$nextSibling.$$prevSibling = this.$$prevSibling;