gridview: Always set header and footer size

Update tile allocation for headers and foots in cases
where we go from having headers to not having headers.

Before this commit, turning sections off in testsections
would leave the global header and footer with some empty
space allocated.

gtk/gtkgridview.c

@@ -929,11 +929,25 @@ gtk_grid_view_size_allocate (GtkWidget *widget,
         {
           if (i > 0)
             i = self->n_columns;
+
+          if (!gtk_list_item_manager_get_has_sections (self->item_manager) && i == 0)
+            gtk_list_tile_set_area_size (self->item_manager,
+                                         tile,
+                                         column_end (self, xspacing, self->n_columns - 1)
+                                         - column_start (self, xspacing, 0),
+                                         0);
         }
       else if (gtk_list_tile_is_header (tile))
         {
           g_assert (i == 0);
           i = self->n_columns;
+
+          if (!gtk_list_item_manager_get_has_sections (self->item_manager))
+            gtk_list_tile_set_area_size (self->item_manager,
+                                         tile,
+                                         column_end (self, xspacing, self->n_columns - 1)
+                                         - column_start (self, xspacing, 0),
+                                         0);
         }
       else
         {