patch 8.2.1491: Vim9: crash when compiling heredoc lines start with comment

Problem:    Vim9: crash when compiling heredoc lines start with comment.
Solution:   Skip over NULL pointers. Do not remove comment and empty lines
            when fetching function lines. (closes #6743)

src/evalfunc.c

@@ -2198,13 +2198,12 @@ execute_redir_str(char_u *value, int value_len)
  * Called by do_cmdline() to get the next line.
  * Returns allocated string, or NULL for end of function.
  */
-
     static char_u *
 get_list_line(
     int	    c UNUSED,
     void    *cookie,
     int	    indent UNUSED,
-    int	    do_concat UNUSED)
+    getline_opt_T options UNUSED)
 {
     listitem_T **p = (listitem_T **)cookie;
     listitem_T *item = *p;