pgmyuvenc: do not create files which are not supported

It is possible to support files with odd width and/or height
if real width and height are stored in header.

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavcodec/pnmenc.c

@@ -69,8 +69,8 @@ static int pnm_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
         n  = avctx->width * 6;
         break;
     case AV_PIX_FMT_YUV420P:
-        if (avctx->width & 1) {
-            av_log(avctx, AV_LOG_ERROR, "pgmyuv needs even width\n");
+        if (avctx->width & 1 || avctx->height & 1) {
+            av_log(avctx, AV_LOG_ERROR, "pgmyuv needs even width and height\n");
             return AVERROR(EINVAL);
         }
         c  = '5';