BSC LCLS: explicitly check for RSL_IE_CHAN_NR

Check that channel number IE is present in the received message. This
fixes following warning:

The value returned by function `@RSL_Types.f_rsl_find_ie' is not used

Change-Id: Icc6824d7acef809d76c70b5ff060a8261a82e2be
Related: OS#3659
diff --git a/bsc/BSC_Tests_LCLS.ttcn b/bsc/BSC_Tests_LCLS.ttcn
index 1c51995..0151329 100644
--- a/bsc/BSC_Tests_LCLS.ttcn
+++ b/bsc/BSC_Tests_LCLS.ttcn
@@ -605,8 +605,11 @@
 	[] CONN_A.receive(tr_RSL_DEACT_SACCH(?));
 	[] CONN_A.receive(tr_RSL_RF_CHAN_REL(?)) -> value rsl {
 		var RSL_IE_Body ieb;
-		f_rsl_find_ie(rsl, RSL_IE_CHAN_NR, ieb);
-		CONN_A.send(ts_RSL_RF_CHAN_REL_ACK(ieb.chan_nr));
+		if (f_rsl_find_ie(rsl, RSL_IE_CHAN_NR, ieb) == true) {
+			CONN_A.send(ts_RSL_RF_CHAN_REL_ACK(ieb.chan_nr));
+		} else {
+			log("Unable to find chan# in RSL_RF_CHAN_REL")
+		}
 		}
 	[] CONN_A.receive(tr_BSSMAP_ClearComplete) {
 		CONN_A.send(BSSAP_Conn_Prim:MSC_CONN_PRIM_DISC_REQ);