[pan] prefs_ui: use GDK_KEY_Escape

[Dominique Dumont <ddumont src gnome org>]

commit fa582623dcf8c1d9352bceba70448ba6cf5a10f2
Author: Dominique Dumont <dod debian org>
Date:   Sun Jun 19 15:05:44 2022 +0200

    prefs_ui: use GDK_KEY_Escape
    
    to port to Gtk3

 pan/gui/prefs-ui.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/pan/gui/prefs-ui.cc b/pan/gui/prefs-ui.cc
index 2c33c0e..b4dfe15 100644
--- a/pan/gui/prefs-ui.cc
+++ b/pan/gui/prefs-ui.cc
@@ -67,7 +67,7 @@ namespace pan
 
     state = event->state & gtk_accelerator_get_default_mod_mask();
 
-    if (event->keyval == GDK_Escape)
+    if (event->keyval == GDK_KEY_Escape)
       return FALSE;    /* close the dialog, don't allow escape when detecting keybindings. */
 
     str = gtk_accelerator_name(event->keyval, GdkModifierType(state));