avformat/rmdec: Use 64bit for intermediate for DEINT_ID_INT4

Fixes: runtime error: signed integer overflow: 65312 * 65535 cannot be represented in type 'int'
Fixes: 32832/clusterfuzz-testcase-minimized-ffmpeg_dem_RM_fuzzer-4817710040088576

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

@@ -267,9 +267,9 @@ static int rm_read_audio_stream_info(AVFormatContext *s, AVIOContext *pb,
         case DEINT_ID_INT4:
             if (ast->coded_framesize > ast->audio_framesize ||
                 sub_packet_h <= 1 ||
-                ast->coded_framesize * sub_packet_h > (2 + (sub_packet_h & 1)) * ast->audio_framesize)
+                ast->coded_framesize * (uint64_t)sub_packet_h > (2 + (sub_packet_h & 1)) * ast->audio_framesize)
                 return AVERROR_INVALIDDATA;
-            if (ast->coded_framesize * sub_packet_h != 2*ast->audio_framesize) {
+            if (ast->coded_framesize * (uint64_t)sub_packet_h != 2*ast->audio_framesize) {
                 avpriv_request_sample(s, "mismatching interleaver parameters");
                 return AVERROR_INVALIDDATA;
             }