avformat/hevc: reject hvcC NAL arrays that overflow the 16-bit count

numNalus is uint16_t; a crafted hvcC declaring >65535 NAL units of one
type wraps it to 0 and then writes nal[-1]. Reject before the count can
wrap. Reachable by remuxing a crafted file with -c copy.

Fixes: integer overflow
Fixes: out of array access

libavformat/hevc.c

@@ -844,6 +844,9 @@ static int hvcc_array_add_nal_unit(const uint8_t *nal_buf, uint32_t nal_size,
     int ret;
     uint16_t numNalus = array->numNalus;
 
+    if (numNalus >= UINT16_MAX)
+        return AVERROR_INVALIDDATA;
+
     ret = av_reallocp_array(&array->nal, numNalus + 1, sizeof(*array->nal));
     if (ret < 0)
         return ret;