avcodec/v4l2_m2m: Simplify capture buffer init check

Before this commit s->avctx == NULL was used to infer that an encoder is
being initialzed. Code readability has been improved by directly using
!av_codec_is_decoder() instead.
Signed-off-by: Andriy Gelman <andriy.gelman@gmail.com>

libavcodec/v4l2_m2m.c

@@ -176,7 +176,7 @@ static int v4l2_configure_contexts(V4L2m2mContext* s)
     }
 
     /* decoder's buffers need to be updated at a later stage */
-    if (!s->avctx || !av_codec_is_decoder(s->avctx->codec)) {
+    if (s->avctx && !av_codec_is_decoder(s->avctx->codec)) {
         ret = ff_v4l2_context_init(&s->capture);
         if (ret) {
             av_log(log_ctx, AV_LOG_ERROR, "no v4l2 capture context's buffers\n");
@@ -307,7 +307,7 @@ int ff_v4l2_m2m_codec_full_reinit(V4L2m2mContext *s)
     }
 
     /* decoder's buffers need to be updated at a later stage */
-    if (!s->avctx || !av_codec_is_decoder(s->avctx->codec)) {
+    if (s->avctx && !av_codec_is_decoder(s->avctx->codec)) {
         ret = ff_v4l2_context_init(&s->capture);
         if (ret) {
             av_log(log_ctx, AV_LOG_ERROR, "no v4l2 capture context's buffers\n");

libavcodec/v4l2_m2m_enc.c

@@ -312,12 +312,12 @@ static av_cold int v4l2_encode_init(AVCodecContext *avctx)
     capture->av_codec_id = avctx->codec_id;
     capture->av_pix_fmt = AV_PIX_FMT_NONE;
 
+    s->avctx = avctx;
     ret = ff_v4l2_m2m_codec_init(priv);
     if (ret) {
         av_log(avctx, AV_LOG_ERROR, "can't configure encoder\n");
         return ret;
     }
-    s->avctx = avctx;
 
     if (V4L2_TYPE_IS_MULTIPLANAR(output->type))
         v4l2_fmt_output = output->format.fmt.pix_mp.pixelformat;