avcodec/cuviddec: add capability check for maximum macroblock count

Cuvid supports clips with a limit on maximum number of macroblocks.
This check was missing after cuvidGetDecoderCaps API call allowing
unsupported clips to proceed.
Added the missing check, same as the one in hwaccel nvdec implementation.
Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>

libavcodec/cuviddec.c

@@ -805,6 +805,12 @@ static int cuvid_test_capabilities(AVCodecContext *avctx,
         return AVERROR(EINVAL);
     }
 
+    if ((probed_width * probed_height) / 256 > caps->nMaxMBCount) {
+        av_log(avctx, AV_LOG_ERROR, "Video macroblock count %d exceeds maximum of %d\n",
+               (int)(probed_width * probed_height) / 256, caps->nMaxMBCount);
+        return AVERROR(EINVAL);
+    }
+
     return 0;
 }