patch 8.2.4458: Vim9: compiling filter() call fails with unknown arguments

Problem:    Vim9: compiling filter() call fails with funcref that has unknown
            arguments.
Solution:   Do not check the arguments if they are unknown at compile time.
            (closes #9835)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index eb42269..e8ed4ba 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -552,6 +552,8 @@
 	    t_func_exp.tt_member = &t_bool;
 	if (args[0] == NULL)
 	    args[0] = &t_unknown;
+	if (type->tt_argcount == -1)
+	    t_func_exp.tt_argcount = -1;
 
 	where.wt_index = 2;
 	return check_type(&t_func_exp, type, TRUE, where);