Show more specific error if no image loaders are available
Don't show unknown format errors if the list of https://docs.rs/glycin/latest/glycin/fn.supported_mime_types.html is empty. Instead, show error that says no loaders are installed.
Don't show unknown format errors if the list of https://docs.rs/glycin/latest/glycin/fn.supported_mime_types.html is empty. Instead, show error that says no loaders are installed.