Fix bug with colliding frames

When you create two spritesheets that use the same source image ( because you want to separate the animations ) the script will fail as the wrong frame is served from cache.

The `frame index number` is not important and collides. 
`regX` and `regY` could be included in the name, but that's just stupid in my opinion, because who uses the same `sourceRect` with different origins for frames?