Don't throw an error when attached picture isn't recognized.

The MIME type field is required per the FLAC standard, but it's
not an error just because ffmpeg doesn't recognize it.
Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/flac_picture.c

@@ -91,8 +91,6 @@ int ff_flac_parse_picture(AVFormatContext *s, uint8_t **bufp, int buf_size,
     if (id == AV_CODEC_ID_NONE) {
         av_log(s, AV_LOG_ERROR, "Unknown attached picture mimetype: %s.\n",
                mimetype);
-        if (s->error_recognition & AV_EF_EXPLODE)
-            return AVERROR_INVALIDDATA;
         return 0;
     }