runtime(netrw): diff (`df`) may open the wrong window (#13275)

closes: #11359

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/autoload/netrw.vim b/runtime/autoload/netrw.vim
index e3ac12f..2358e26 100644
--- a/runtime/autoload/netrw.vim
+++ b/runtime/autoload/netrw.vim
@@ -7392,8 +7392,7 @@
      exe "NetrwKeepj e ".fnameescape(fname)
      diffthis
     elseif cnt == 2 || cnt == 3
-     vsplit
-     wincmd l
+     below vsplit
 "     call Decho("diffthis: ".fname,'~'.expand("<slnum>"))
      exe "NetrwKeepj e ".fnameescape(fname)
      diffthis