library/L3_Templates.ttcn: fix length matching in tr_RP_ERROR_MT

Change-Id: Id5a4210a9f256f8bd7b0048fd65610de8c378bb9
diff --git a/library/L3_Templates.ttcn b/library/L3_Templates.ttcn
index 6b5f5c2..cf7b9d9 100644
--- a/library/L3_Templates.ttcn
+++ b/library/L3_Templates.ttcn
@@ -2996,7 +2996,7 @@
 		rP_Spare := '00000'B,
 		rP_Message_Reference := msg_ref,
 		rP_CauseLV := {
-			rP_LengthIndicator := 0, /* overwritten */
+			rP_LengthIndicator := ?,
 			rP_CauseV := {
 				causeValue := f_cause_or_wc(cause),
 				ext := '0'B