ran-emu: allow receiving Paging without a TMSI

Fix access of non-present tMSI.* if tMSI == omit, allowing to match
incoming Paging with a UnitData receiver that has no TMSI.

Change-Id: I1bdf3488be0f8d4f0905665c4ba642f9468b9777
diff --git a/library/RAN_Emulation.ttcnpp b/library/RAN_Emulation.ttcnpp
index 5b2f190..fbe921d 100644
--- a/library/RAN_Emulation.ttcnpp
+++ b/library/RAN_Emulation.ttcnpp
@@ -504,8 +504,11 @@
 runs on RAN_Emulation_CT return template PDU_BSSAP {
 	if (match(bssap, tr_BSSMAP_Paging)) {
 		var RAN_ConnHdlr client := null;
-		client := f_imsi_table_find(bssap.pdu.bssmap.paging.iMSI.digits,
-					   bssap.pdu.bssmap.paging.tMSI.tmsiOctets);
+		var template OCT4 tmsi := omit;
+		if (ispresent(bssap.pdu.bssmap.paging.tMSI)) {
+			tmsi := bssap.pdu.bssmap.paging.tMSI.tmsiOctets;
+		}
+		client := f_imsi_table_find(bssap.pdu.bssmap.paging.iMSI.digits, tmsi);
 		if (client != null) {
 			log("CommonBssmapUnitdataCallback: IMSI/TMSI found in table, dispatching to ",
 				client);