transcode: video: don't wait for drain to update output

Fix a regression introduced by d8c883e2
where video processing was waiting for drain input to feed the output
frame chain.

This goes back to the previous behaviour where transcode input also
unloads the decoder output fifo and sends it.

modules/stream_out/transcode/video.c

@@ -559,13 +559,14 @@ int transcode_video_process( sout_stream_t *p_stream, sout_stream_id_sys_t *id,
     if( ret != VLCDEC_SUCCESS )
         return VLC_EGENERIC;
 
-    /* Only drain if we drained the decoder too. */
-    if (in != NULL)
+    /*
+     * Encoder creation depends on decoder's update_format which is only
+     * created once a few frames have been passed to the decoder.
+     */
+    if( id->encoder == NULL )
         return VLC_SUCCESS;
 
-    /* Drain encoder */
     vlc_fifo_Lock( id->output_fifo );
-    assert(id->encoder);
     if( unlikely( !id->b_error && in == NULL ) && transcode_encoder_opened( id->encoder ) )
     {
         msg_Dbg( p_stream, "Flushing thread and waiting that");