[gtk/gtk-3-22] printing: Be more careful when deserializing

[Matthias Clasen <matthiasc src gnome org>]

commit 21fddc3994e5405cc914fd427aa8572f652d05aa
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Apr 20 16:56:28 2018 -0400

    printing: Be more careful when deserializing
    
    The GVariant we are getting here might not be coming
    from GTK+, but rather from some other source. Best to
    be forgiving and deal with missing data without crashing.
    
    This was causing the GTK+ portal backends to crash on
    print requests from Qt.

 gtk/gtkpagesetup.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkpagesetup.c b/gtk/gtkpagesetup.c
index 9c81343745..e1cbeb8573 100644
--- a/gtk/gtkpagesetup.c
+++ b/gtk/gtkpagesetup.c
@@ -902,8 +902,11 @@ gtk_page_setup_new_from_gvariant (GVariant *variant)
   setup = gtk_page_setup_new ();
 
   paper_size = gtk_paper_size_new_from_gvariant (variant);
-  gtk_page_setup_set_paper_size (setup, paper_size);
-  gtk_paper_size_free (paper_size);
+  if (paper_size)
+    {
+      gtk_page_setup_set_paper_size (setup, paper_size);
+      gtk_paper_size_free (paper_size);
+    }
 
   if (g_variant_lookup (variant, "MarginTop", "d", &margin))
     gtk_page_setup_set_top_margin (setup, margin, GTK_UNIT_MM);