Redraw the header after size allocation of the sheet.

If the horizontal scrollbar is visible, the header foreground colour is
wrong so add a redraw of the header at the end of the allocate.

gnucash/register/register-gnome/gnucash-sheet.c

@@ -1118,7 +1118,7 @@ gnucash_sheet_size_allocate (GtkWidget *widget, GtkAllocation *allocation)
             gnucash_sheet_show_row (sheet,
                                     virt_loc.vcell_loc.virt_row);
     }
-
+    gnc_header_request_redraw (GNC_HEADER(sheet->header_item));
     LEAVE(" ");
 }