fix($cacheFactory): return undefined when removing non-existent entry

Instead of throwning an exception, remove should return undefined when
cache entry to be removed doesn't exist.

Closes #1497

Author: jtymes

src/ng/cacheFactory.js

@@ -70,6 +70,8 @@ function $CacheFactoryProvider() {
         remove: function(key) {
           var lruEntry = lruHash[key];
 
+          if (!lruEntry) return;
+
           if (lruEntry == freshEnd) freshEnd = lruEntry.p;
           if (lruEntry == staleEnd) staleEnd = lruEntry.n;
           link(lruEntry.n,lruEntry.p);

test/ng/cacheFactorySpec.js

@@ -89,6 +89,11 @@ describe('$cacheFactory', function() {
       }));
 
 
+      it('should return undefined when entry does not exist', inject(function($cacheFactory) {
+        expect(cache.remove('non-existent')).toBeUndefined();
+      }));
+
+
       it('should stringify keys', inject(function($cacheFactory) {
         cache.put('123', 'foo');
         cache.put(123, 'bar');