Retrieves a static image for the animation.
If an animation is really just a plain image (has only one frame), this function returns that image.
If the animation is an animation, this function returns a reasonable image to use as a static unanimated image, which might be the first frame, or something more sophisticated depending on the file format.
If an animation hasn't loaded any frames yet, this function will return `NULL`.
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unanimated image representing the animation |