vim-patch:8.2.0810: error when appending "tagfile" to 'wildoptions'

Problem:    Error when appending "tagfile" to 'wildoptions'.
Solution:   use flags P_ONECOMMA and P_NODUP. (Dmitri Vereshchagin,
            closes vim/vim#6105)
2e61e2d083

src/nvim/testdir/test_options.vim

@@ -42,6 +42,13 @@ function Test_wildchar()
   set wildchar&
 endfunction
 
+func Test_wildoptions()
+  set wildoptions=
+  set wildoptions+=tagfile
+  set wildoptions+=tagfile
+  call assert_equal('tagfile', &wildoptions)
+endfunc
+
 function! Test_options()
   let caught = 'ok'
   try