Missing return in an function prevents image being delivered in first hit

Hi, first of all, thank you for this nice module.

I found a bug on image_animgif_save() that prevents the image of being delivered on the first hit of the image style.

The image_save function expects a return value from image_animgif_save() to be returned in order to tell its caller if the image was saved with success. The function image_animgif_save() does not return any value, therefore the core image module things that the image was not created (image_style_deliver()).