Do not skip three bytes and don't search for extradata in old realaudio files.

Fixes ticket #1557.

libavformat/rmdec.c

@@ -196,6 +196,9 @@ static int rm_read_audio_stream_info(AVFormatContext *s, AVIOContext *pb,
             st->need_parsing = AVSTREAM_PARSE_HEADERS;
         case AV_CODEC_ID_ATRAC3:
         case AV_CODEC_ID_SIPR:
+            if (read_all) {
+                codecdata_length = 0;
+            } else {
             avio_rb16(pb); avio_r8(pb);
             if (version == 5)
                 avio_r8(pb);
@@ -204,6 +207,7 @@ static int rm_read_audio_stream_info(AVFormatContext *s, AVIOContext *pb,
                 av_log(s, AV_LOG_ERROR, "codecdata_length too large\n");
                 return -1;
             }
+            }
 
             ast->audio_framesize = st->codec->block_align;
             if (st->codec->codec_id == AV_CODEC_ID_SIPR) {