avcodec/encode: Avoid check whose result is known in advance

encode_send_frame_internal() is always only called if
the buffer packet is empty and except when we are dealing
with an audio codec that does not allow variable frame size
it stays that way until a call to av_frame_ref() at the end
of encode_send_frame_internal(). In case we are dealing
with the small last frame of an audio encoder requiring
constant frame size the frame will be allocated by pad_last_frame()
and this the only case where this is so. So by returning directly
after pad_last_frame(), we can avoid having to recheck
whether the frame is still empty before av_frame_ref().

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/encode.c

@@ -339,6 +339,7 @@ static int encode_send_frame_internal(AVCodecContext *avctx, const AVFrame *src)
                     return ret;
 
                 avctx->internal->last_audio_frame = 1;
+                return 0;
             } else if (src->nb_samples > avctx->frame_size) {
                 av_log(avctx, AV_LOG_ERROR, "nb_samples (%d) != frame_size (%d)\n", src->nb_samples, avctx->frame_size);
                 return AVERROR(EINVAL);
@@ -346,11 +347,9 @@ static int encode_send_frame_internal(AVCodecContext *avctx, const AVFrame *src)
         }
     }
 
-    if (!dst->data[0]) {
     ret = av_frame_ref(dst, src);
     if (ret < 0)
         return ret;
-    }
 
     return 0;
 }