avcodec/h264_parser: Fix nalsize check

Fixes: Assertion failure
Fixes: 37463/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_H264_fuzzer-4914693494931456

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

libavcodec/h264_parser.c

@@ -83,12 +83,12 @@ static int h264_find_frame_end(H264ParseContext *p, const uint8_t *buf,
 
     for (i = 0; i < buf_size; i++) {
         if (i >= next_avc) {
-            uint32_t nalsize = 0;
+            int64_t nalsize = 0;
             i = next_avc;
             for (j = 0; j < p->nal_length_size; j++)
                 nalsize = (nalsize << 8) | buf[i++];
             if (!nalsize || nalsize > buf_size - i) {
-                av_log(logctx, AV_LOG_ERROR, "AVC-parser: nal size %"PRIu32" "
+                av_log(logctx, AV_LOG_ERROR, "AVC-parser: nal size %"PRId64" "
                        "remaining %d\n", nalsize, buf_size - i);
                 return buf_size;
             }