fix($observe): check if the attribute is undefined

Check if the attribute is undefined before manually applying the function because if not an
undefined property is added to the scope of the form controller when the input control does not
have a name.

Closes angular#9707
Closes angular#9720

Author: Puigcerber

src/ng/compile.js

@@ -1072,7 +1072,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
         listeners.push(fn);
         $rootScope.$evalAsync(function() {
-          if (!listeners.$$inter) {
+          if (!listeners.$$inter && attrs.hasOwnProperty(key)) {
             // no one registered attribute interpolation function, so lets call it manually
             fn(attrs[key]);
           }

test/ng/directive/inputSpec.js

@@ -1331,6 +1331,24 @@ describe('input', function() {
     expect(scope.name).toEqual('adam');
   });
 
+
+  it('should not add the property to the scope if name is unspecified', function() {
+    inputElm = jqLite('<input type="text" ng-model="name">');
+    formElm = jqLite('<form name="form"></form>');
+    formElm.append(inputElm);
+    $compile(formElm)(scope);
+
+    spyOn(scope.form, '$addControl').andCallThrough();
+    spyOn(scope.form, '$$renameControl').andCallThrough();
+
+    scope.$digest();
+
+    expect(scope.form['undefined']).toBeUndefined();
+    expect(scope.form.$addControl).not.toHaveBeenCalled();
+    expect(scope.form.$$renameControl).not.toHaveBeenCalled();
+  });
+
+
   describe('compositionevents', function() {
     it('should not update the model between "compositionstart" and "compositionend" on non android', inject(function($sniffer) {
       $sniffer.android = false;