patch 8.2.0529: Vim9: function argument with default not checked

Problem:    Vim9: function argument with default not checked.
Solution:   Check type of argument with default value.
diff --git a/src/userfunc.c b/src/userfunc.c
index 69a57c2..316eac6 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -3045,8 +3045,8 @@
 		{
 		    p = ((char_u **)argtypes.ga_data)[i];
 		    if (p == NULL)
-			// todo: get type from default value
-			type = &t_any;
+			// will get the type from the default value
+			type = &t_unknown;
 		    else
 			type = parse_type(&p, &fp->uf_type_list);
 		    if (type == NULL)