transcode: fix crash on eof when using threads >=1

For now do not flush encoder buffers (as added in [14054532]), but
ideally that should be fixed

modules/stream_out/transcode/video.c

@@ -596,6 +596,8 @@ int transcode_video_process( sout_stream_t *p_stream, sout_stream_id_t *id,
     *out = NULL;
 
     if( in == NULL )
+    {
+        if( p_sys->i_threads == 0 )
         {
             block_t *p_block;
             do {
@@ -604,6 +606,14 @@ int transcode_video_process( sout_stream_t *p_stream, sout_stream_id_t *id,
                 video_timer_stop( id->p_encoder );
                 block_ChainAppend( out, p_block );
             } while( p_block );
+        }
+        else
+        {
+            /*
+             * FIXME: we need EncoderThread() to flush buffers and signal us
+             * when it's done so we can send the last frames to the chain
+             */
+        }
         return VLC_SUCCESS;
     }