demux_lavf: always give libavformat the filename when probing

This gives the filename or URL to the libavformat probing logic, which
might use the file extension as a "help" to decide which format the file
is. This helps with mp3 files that have large id3v2 tags and prevents
the idiotic ffmpeg probing logic to think that a mp3 file is amr.

(What we really want is knowing whether we _really_ need to feed more
data to libavformat to detect the format. And without having to pre-read
excessive amounts of data for relatively normal streams.)

demux/demux_lavf.c

@@ -403,7 +403,7 @@ static int lavf_check_file(demuxer_t *demuxer, enum demux_check check)
 
     AVProbeData avpd = {
         // Disable file-extension matching with normal checks
-        .filename = check <= DEMUX_CHECK_REQUEST ? priv->filename : "",
+        .filename = priv->filename,
         .buf_size = 0,
         .buf = av_mallocz(PROBE_BUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE),
     };