avformat/dxa: avoid bpc overflows

Fixes: signed integer overflow: 2147483647 + 32 cannot be represented in type 'int'
Fixes: 50993/clusterfuzz-testcase-minimized-ffmpeg_dem_DXA_fuzzer-6639823726706688

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

libavformat/dxa.c

@@ -118,9 +118,12 @@ static int dxa_read_header(AVFormatContext *s)
             if(tag == MKTAG('d', 'a', 't', 'a')) break;
             avio_skip(pb, fsize);
         }
-        c->bpc = (fsize + c->frames - 1) / c->frames;
-        if(ast->codecpar->block_align)
+        c->bpc = (fsize + (int64_t)c->frames - 1) / c->frames;
+        if(ast->codecpar->block_align) {
+            if (c->bpc > INT_MAX - ast->codecpar->block_align + 1)
+                return AVERROR_INVALIDDATA;
             c->bpc = ((c->bpc + ast->codecpar->block_align - 1) / ast->codecpar->block_align) * ast->codecpar->block_align;
+        }
         c->bytes_left = fsize;
         c->wavpos = avio_tell(pb);
         avio_seek(pb, c->vidpos, SEEK_SET);