avcodec/libx265: zero the padding bytes in extradata

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/libx265.c

@@ -400,6 +400,7 @@ static av_cold int libx265_encode_init(AVCodecContext *avctx)
         }
 
         memcpy(avctx->extradata, nal[0].payload, avctx->extradata_size);
+        memset(avctx->extradata + avctx->extradata_size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
     }
 
     return 0;