spice server: try to be less brutal when changing res or when flushing the tree

The idea is that we can try to defer some stuff to be later
send in the pipe if the pipe is not fulled yet, moreover
we will then walk on the pipe using:
red_clear_surface_drawables_from_pipe() and will try to
remove the uneeded objects of this surface

Still some room to improvment but later...

Signed-off-by: Izik Eidus <ieidus@redhat.com>

server/red_worker.c

@@ -8143,6 +8143,11 @@ static inline void flush_display_commands(RedWorker *worker)
     for (;;) {
         uint64_t end_time;
 
+        red_process_commands(worker, MAX_PIPE_SIZE);
+        if (!worker->qxl->has_command(worker->qxl)) {
+            break;
+        }
+
         while (red_process_commands(worker, MAX_PIPE_SIZE)) {
             display_channel_push(worker);
         }