Elm Image: fix usage of animated gif on the same image object more than one time

Elm Image: fix usage of animated gif on the same image object more than one time

This patch @fix this usage example:

0. image obj create
1. file_set(an animated gif)
2. animated_set(TRUE) + animated_play_set(TRUE) to make the gif play
3. file_set(a normal image)
... at this point elm_image is confused because it still think that the image is animated
4. file_set(an animated gif)
5. animated_set(TRUE) + animated_play_set(TRUE) to make the gif play
...this now do not work because elm think that the image is already animated