[balsa/gtk4: 154/196] toolbar-prefs: Center the arrows vertically

[Peter Bloomfield <peterb src gnome org>]

commit d0520ed86cd600fa4342de086e9be240f714caa6
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Sun Aug 30 12:01:38 2020 -0400

    toolbar-prefs: Center the arrows vertically
    
    Vertically center the box containing the four arrow buttons; it had
    somehow floated up to the top of the column.

 src/toolbar-prefs.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/src/toolbar-prefs.c b/src/toolbar-prefs.c
index c9eaf87d2..5a7b9ab42 100644
--- a/src/toolbar-prefs.c
+++ b/src/toolbar-prefs.c
@@ -460,8 +460,9 @@ create_toolbar_page(BalsaToolbarModel * model, GActionMap * map)
     center_button_box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
     gtk_container_add(GTK_CONTAINER(lower_ctlbox), center_button_box);
 
-    gtk_container_add(GTK_CONTAINER(lower_ctlbox), center_button_box);
-
+    button_box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
+    gtk_widget_set_vexpand(button_box, TRUE);
+    gtk_widget_set_valign(button_box, GTK_ALIGN_CENTER);
     gtk_container_add(GTK_CONTAINER(center_button_box), button_box);
 
     page->back_button =