avcodec/dpx: Check bits_per_color earlier

Fixes: shift exponent 251 is too large for 32-bit type 'int'
Fixes: 32147/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DPX_fuzzer-5519111675314176

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

libavcodec/dpx.c

@@ -242,6 +242,9 @@ static int decode_frame(AVCodecContext *avctx,
         return AVERROR_PATCHWELCOME;
     }
 
+    if (bits_per_color > 32)
+        return AVERROR_INVALIDDATA;
+
     buf += 820;
     avctx->sample_aspect_ratio.num = read32(&buf, endian);
     avctx->sample_aspect_ratio.den = read32(&buf, endian);