vim-patch:9.0.0656: cannot specify another character to use instead of '@'

Problem:    Cannot specify another character to use instead of '@' at the end
            of the window.
Solution:   Add "lastline" to 'fillchars'. (Martin Tournoij, closes vim/vim#11264,
            closes vim/vim#10963)
4ba5f1dab6

Use latest code in drawscreen.c instead.

src/nvim/screen.c

@@ -1328,6 +1328,7 @@ char *set_chars_option(win_T *wp, char **varp, bool apply)
     { &wp->w_p_fcs_chars.diff,       "diff",      '-' },
     { &wp->w_p_fcs_chars.msgsep,     "msgsep",    ' ' },
     { &wp->w_p_fcs_chars.eob,        "eob",       '~' },
+    { &wp->w_p_fcs_chars.lastline,   "lastline",  '@' },
   };
 
   struct chars_tab lcs_tab[] = {