fix for ng:include does not remove partial if src goes to undefined

Author: IgorMinar

src/widgets.js

@@ -260,6 +260,8 @@ angularWidget('ng:include', function(element){
             compiler.compile(element)(element, childScope);
             childScope.$init();
           });
+        } else {
+          element.html('');
         }
       });
     };

test/widgetsSpec.js

@@ -436,6 +436,21 @@ describe("widget", function(){
       scope.$init();
       expect(element.text()).toEqual('misko');
     });
+
+    it('should remove previously included text if a falsy value is bound to src', function() {
+      var element = jqLite('<ng:include src="url" scope="childScope"></ng:include>');
+      var scope = angular.compile(element);
+      scope.childScope = createScope();
+      scope.childScope.name = 'igor';
+      scope.url = 'myUrl';
+      scope.$xhr.cache.data.myUrl = {value:'{{name}}'};
+      scope.$init();
+
+      scope.url = undefined;
+      scope.$eval();
+      
+      expect(element.text()).toEqual('');
+    });
   });
 });