[gtk/gtk-3-24] [quartz] Fix use-before-init.

[John Ralls <jralls src gnome org>]

commit 07d847d174feabd602787ce04b15784b96f0980a
Author: John Ralls <jralls ceridwen us>
Date:   Mon Feb 28 10:05:47 2022 -0800

    [quartz] Fix use-before-init.
    
    Thanks to Lukas Oberhuber for the patch.
    
    Fixes https://gitlab.gnome.org/GNOME/gtk/-/issues/4726

 gdk/quartz/gdkmonitor-quartz.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gdk/quartz/gdkmonitor-quartz.c b/gdk/quartz/gdkmonitor-quartz.c
index f3f99a583e..5d79a8ea33 100644
--- a/gdk/quartz/gdkmonitor-quartz.c
+++ b/gdk/quartz/gdkmonitor-quartz.c
@@ -33,7 +33,7 @@ gdk_quartz_monitor_get_workarea (GdkMonitor   *monitor,
   GDK_QUARTZ_ALLOC_POOL;
 
   NSArray *array = [NSScreen screens];
-  NSScreen* screen;
+  NSScreen* screen = NULL;
   for (id obj in array)
     {
       CGDirectDisplayID screen_id =