avformat/xmv: Make bitrate 64bit

Fixes: signed integer overflow: 32 * 538976288 cannot be represented in type 'int'
Fixes: 15633/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5752273981931520

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

libavformat/xmv.c

@@ -79,7 +79,7 @@ typedef struct XMVAudioPacket {
     uint16_t channels;        ///< Number of channels.
     int32_t sample_rate;      ///< Sampling rate.
     uint16_t bits_per_sample; ///< Bits per compressed sample.
-    uint32_t bit_rate;        ///< Bits of compressed data per second.
+    uint64_t bit_rate;        ///< Bits of compressed data per second.
     uint16_t flags;           ///< Flags
     unsigned block_align;     ///< Bytes per compressed block.
     uint16_t block_samples;   ///< Decompressed samples per compressed block.
@@ -191,7 +191,7 @@ static int xmv_read_header(AVFormatContext *s)
         packet->bits_per_sample = avio_rl16(pb);
         packet->flags           = avio_rl16(pb);
 
-        packet->bit_rate      = packet->bits_per_sample *
+        packet->bit_rate      = (uint64_t)packet->bits_per_sample *
                                 packet->sample_rate *
                                 packet->channels;
         packet->block_align   = XMV_BLOCK_ALIGN_SIZE * packet->channels;