Fixes issue that caused graphics loading to fail when only using @1x …

…graphics in an atlas sprite asset.

cocos2d/CCSpriteFrameCache.m

@@ -445,7 +445,7 @@ -(void) addSpriteFramesFromSpriteAtlasAssetNamed:(NSString *)atlasAssetName
 
         if (indexes.count == 0) {
             // Falling back to using @1x graphics if the expected resolution is not found.
-            [indexes addIndexes:[self indexesForImagePaths:imagePaths forFilename:atlasAssetName withSuffix:nil]];
+            [indexes addIndexes:[self indexesForImagePaths:imagePaths forFilename:atlasAssetName withSuffix:@""]];
             scaleSuffix = nil;
         }