[gnome-nibbles/arnaudb/wip/gtk4: 139/188] Replace GdkScreen by GdkDisplay.

[Arnaud B. <arnaudb src gnome org>]

commit 3cb8690c7279ed5e77dc182ca5efc17a16ea10bf
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Mon May 25 14:44:24 2020 +0200

    Replace GdkScreen by GdkDisplay.

 src/gnome-nibbles.vala | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/gnome-nibbles.vala b/src/gnome-nibbles.vala
index ee5d926..960c653 100644
--- a/src/gnome-nibbles.vala
+++ b/src/gnome-nibbles.vala
@@ -174,7 +174,9 @@ private class Nibbles : Gtk.Application
 
         var css_provider = new CssProvider ();
         css_provider.load_from_resource ("/org/gnome/Nibbles/ui/nibbles.css");
-        StyleContext.add_provider_for_screen (Gdk.Screen.get_default (), css_provider, 
STYLE_PROVIDER_PRIORITY_APPLICATION);
+        Gdk.Display? gdk_display = Gdk.Display.get_default ();
+        if (gdk_display != null) // else..?
+            StyleContext.add_provider_for_display ((!) gdk_display, css_provider, 
STYLE_PROVIDER_PRIORITY_APPLICATION);
 
         add_action_entries (action_entries, this);