fix(ngAnimate): properly handle empty jqLite collections

Previously `stripCommentsFromElement()` would return an empty Array (instead of a jqLite collection)
which would cause an exception to be thrown: "element.parent not a function".
This commit fixes it, by ensuring that the returned value is always a jqLite collection.

Closes angular#14558

Closes angular#14559

Author: maksimr

src/ngAnimate/shared.js

@@ -127,7 +127,7 @@ function stripCommentsFromElement(element) {
   if (element instanceof jqLite) {
     switch (element.length) {
       case 0:
-        return [];
+        return element;
         break;
 
       case 1:

test/ngAnimate/animateSpec.js

@@ -414,6 +414,19 @@ describe("animations", function() {
       expect(capturedAnimation).toBeFalsy();
     }));
 
+    it('should not attempt to perform an animation on an empty jqLite collection',
+      inject(function($rootScope, $animate) {
+
+        element.html('');
+        var emptyNode = jqLite(element[0].firstChild);
+
+        $animate.addClass(emptyNode, 'some-class');
+        $rootScope.$digest();
+
+        expect(capturedAnimation).toBeFalsy();
+      })
+    );
+
     it('should perform the leave domOperation if a text node is used',
       inject(function($rootScope, $animate) {