avformat/rmdec: sanity check coded_framesize

Fixes: signed integer overflow: -14671840 * 8224 cannot be represented in type 'int'
Fixes: 24793/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5101884323659776

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rmdec.c

@@ -165,7 +165,11 @@ static int rm_read_audio_stream_info(AVFormatContext *s, AVIOContext *pb,
         avio_rb16(pb); /* version2 */
         avio_rb32(pb); /* header size */
         flavor= avio_rb16(pb); /* add codec info / flavor */
-        ast->coded_framesize = coded_framesize = avio_rb32(pb); /* coded frame size */
+        coded_framesize = avio_rb32(pb); /* coded frame size */
+        if (coded_framesize < 0)
+            return AVERROR_INVALIDDATA;
+        ast->coded_framesize = coded_framesize;
+
         avio_rb32(pb); /* ??? */
         bytes_per_minute = avio_rb32(pb);
         if (version == 4) {