[mutter/gnome-3-36] x11: Finish INCR transfers properly

[Robert Mader <rmader src gnome org>]

commit c43f178495a1ad653e7d2e3a4624b1f93731dd61
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat Apr 11 17:12:18 2020 +0200

    x11: Finish INCR transfers properly
    
    INCR transfers are mandated to finish with a final 0-size XChangeProperty
    roundtrip after the final data chunk. Actually honor this and ensure we
    iterate just once more for this.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1198
    
    (cherry picked from commit 04d429b743a641c81e2fd8b683a8ec40775b3213)

 src/x11/meta-x11-selection-output-stream.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/src/x11/meta-x11-selection-output-stream.c b/src/x11/meta-x11-selection-output-stream.c
index 59ca1d400..c6df055b4 100644
--- a/src/x11/meta-x11-selection-output-stream.c
+++ b/src/x11/meta-x11-selection-output-stream.c
@@ -125,7 +125,12 @@ meta_x11_selection_output_stream_needs_flush_unlocked (MetaX11SelectionOutputStr
     meta_x11_selection_output_stream_get_instance_private (stream);
 
   if (priv->data->len == 0)
-    return FALSE;
+    {
+      if (priv->incr)
+        return g_output_stream_is_closing (G_OUTPUT_STREAM (stream));
+      else
+        return FALSE;
+    }
 
   if (g_output_stream_is_closing (G_OUTPUT_STREAM (stream)))
     return TRUE;