Commit a46ab2ced20d757e0e770d4de1edc3a152cc4f2f introduced a regression, breaking typefinding for media content muxed in mp4 container and serialized to data URIs. For this case it doesn't make sense to look for a file extension, so skip URI parsing. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1909>