runtime(netrw): using inefficient highlight pattern for 'mf'

Fixes E872 too many '(' in highlight pattern for `mf` selection

fixup for #15551
closes: #15700

Signed-off-by: yasuda <yasuda@kyoto-sr.co.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/autoload/netrw.vim b/runtime/autoload/netrw.vim
index fef151a..b4a70e1 100644
--- a/runtime/autoload/netrw.vim
+++ b/runtime/autoload/netrw.vim
@@ -24,6 +24,7 @@
 "   2024 Aug 22 by Vim Project: fix mf-selection highlight (#15551)
 "   2024 Aug 22 by Vim Project: adjust echo output of mx command (#15550)
 "   2024 Sep 15 by Vim Project: more strict confirmation dialog (#15680)
+"   2024 Sep 19 by Vim Project: mf-selection highlight uses wrong pattern (#15700)
 "   }}}
 " Former Maintainer:	Charles E Campbell
 " GetLatestVimScripts: 1075 1 :AutoInstall: netrw.vim
@@ -6890,7 +6891,7 @@
 
   let ykeep   = @@
   let curbufnr= bufnr("%")
-  let leader= '\(^\|\s\)\zs'
+  let leader= '\%(^\|\s\)\zs'
   if a:fname =~ '\a$'
    let trailer = '\>[@=|\/\*]\=\ze\%(  \|\t\|$\)'
   else