patch 9.1.0988: Vim9: no error when using uninitialized var in new()

Problem:  Vim9: no error when using uninitialized var in new()
          (lifepillar, Aliaksei Budavei)
Solution: Give an error if an uninitialized object variable is referenced
          in new() (Yegappan Lakshmanan)

fixes: #14411
fixes: #16344
closes: #16374

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/errors.h b/src/errors.h
index 1e59597..ad36e33 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3616,8 +3616,10 @@
 	INIT(= N_("E1428: Duplicate enum value: %s"));
 EXTERN char e_class_can_only_be_used_in_script[]
 	INIT(= N_("E1429: Class can only be used in a script"));
+EXTERN char e_uninitialized_object_var_reference[]
+	INIT(= N_("E1430: Uninitialized object variable '%s' referenced"));
 #endif
-// E1429 - E1499 unused (reserved for Vim9 class support)
+// E1431 - E1499 unused (reserved for Vim9 class support)
 EXTERN char e_cannot_mix_positional_and_non_positional_str[]
 	INIT(= N_("E1500: Cannot mix positional and non-positional arguments: %s"));
 EXTERN char e_fmt_arg_nr_unused_str[]