Uploading a GIF results in ArgumentCountError

[nu111]

https://github.com/psolom/RichFilemanager-PHP/blob/master/src/Repository/BaseUploadHandler.php#L791

when uploading a GIF, this error is thrown

ArgumentCountError: imagegif() expects at most 2 arguments, 3 given

I think that this behaviour is related to changes since php 7.1.

Maybe the clearest fix would be to break the

return $write_func($src_img, $new_file_path, $image_quality);

into a switch.

This is a remainder, I will try to fix it later on.