Avoid creating an animated image for 1-frame GIFs

When loading *GIFs* with just 1 frame the

     [UIImage animatedImageWithImages:duration:]

constructor was being used, and `UIImage`'s `images` property was returning an array with only one element.

I think that when loading GIFs with just 1 frame they should load as regular non-animated images. I modified the code so that's the case.

Also added some test logs to check the `images` property values for 1-framed GIF and for a PNG file.