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)
diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index b993ef2..3977c4d 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -1867,7 +1867,7 @@
     int		bad_char;	// BAD_KEEP, BAD_DROP or replacement byte
     int		useridx;	// user command index
     char	*errmsg;	// returned error message
-    char_u	*(*getline)(int, void *, int, int);
+    char_u	*(*getline)(int, void *, int, getline_opt_T);
     void	*cookie;	// argument for getline()
 #ifdef FEAT_EVAL
     cstack_T	*cstack;	// condition stack for ":if" etc.