Avoid errors in old versions of vim

vim/.config/vim/init.d/xdg.vim

@@ -9,12 +9,31 @@ set runtimepath+=$XDG_CONFIG_HOME/vim/after
 set runtimepath+=$XDG_DATA_HOME/vim
 
 set packpath^=$XDG_DATA_HOME/vim
+
+if !isdirectory($XDG_DATA_HOME.'/vim/spell')
   call mkdir($XDG_DATA_HOME.'/vim/spell', 'p', 0700)
+endif
+
+set backupdir=$XDG_CACHE_HOME/vim/backup/
+set directory=$XDG_CACHE_HOME/vim/swap/
+set undodir=$XDG_CACHE_HOME/vim/undo/
+set viewdir=$XDG_CACHE_HOME/vim/view/
+
+if !isdirectory(&backupdir)
+  call mkdir(&backupdir, 'p', 0700)
+endif
 
-set backupdir=$XDG_CACHE_HOME/vim/backup//  | call mkdir(&backupdir, 'p', 0700)
-set directory=$XDG_CACHE_HOME/vim/swap//    | call mkdir(&directory, 'p', 0700)
-set undodir=$XDG_CACHE_HOME/vim/undo//      | call mkdir(&undodir,   'p', 0700)
-set viewdir=$XDG_CACHE_HOME/vim/view//      | call mkdir(&viewdir,   'p', 0700)
+if !isdirectory(&directory)
+  call mkdir(&directory, 'p', 0700)
+endif
+
+if !isdirectory(&undodir)
+  call mkdir(&undodir,   'p', 0700)
+endif
+
+if !isdirectory(&viewdir)
+  call mkdir(&viewdir,   'p', 0700)
+endif
 
 if !has('nvim')
   set viminfofile=$XDG_CACHE_HOME/vim/viminfo