[gtk/matthiasc/for-master] center layout: Fix handling of expanding center child

[Matthias Clasen <matthiasc src gnome org>]

commit 2d3885a44ab3c9c815d15b4f9571c2161599f7fb
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jan 1 11:02:57 2021 -0500

    center layout: Fix handling of expanding center child
    
    We were not taking spacing into account when adjusting
    the size of an expanding center child, causing it to slip
    under the end child at times.
    
    Fixes: #3506

 gtk/gtkcenterlayout.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtkcenterlayout.c b/gtk/gtkcenterlayout.c
index f9fa988ca7..b2dee1db0d 100644
--- a/gtk/gtkcenterlayout.c
+++ b/gtk/gtkcenterlayout.c
@@ -177,7 +177,7 @@ gtk_center_layout_distribute (GtkCenterLayout  *self,
         center_pos = size - center_size - end_size - spacing;
       else if (center_expand)
         {
-          center_size = size - 2 * MAX (start_size, end_size);
+          center_size = size - 2 * (MAX (start_size, end_size) + spacing);
           center_pos = (size / 2) - (center_size / 2) + spacing;
         }