runtime: Set b:undo_ftplugin where missing (#12943)

Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/ftplugin/abap.vim

@@ -3,6 +3,7 @@
 " Author:	Steven Oliver <oliver.steven@gmail.com>
 " Copyright:	Copyright (c) 2013 Steven Oliver
 " License:	You may redistribute this under the same terms as Vim itself
+" Last Change:  2023 Aug 28 by Vim Project (undo_ftplugin)
 " --------------------------------------------------------------------------
 
 " Only do this when not done yet for this buffer
@@ -17,10 +18,13 @@ set cpo&vim
 setlocal softtabstop=2 shiftwidth=2
 setlocal suffixesadd=.abap
 
+let b:undo_ftplugin = "setl sts< sua< sw<"
+
 " Windows allows you to filter the open file dialog
 if has("gui_win32") && !exists("b:browsefilter")
   let b:browsefilter = "ABAP Source Files (*.abap)\t*.abap\n" .
                      \ "All Files (*.*)\t*.*\n"
+  let b:undo_ftplugin .= " | unlet! b:browsefilter"
 endif
 
 let &cpo = s:cpo_save