bsc: Fix f_establish_fully() for cases where we expect ASSIGN FAIL

When f_ass_patch_lcls() was recently introduced during LCLS support
patches, we broke any testcases that *expected* an ASSIGNMENT FAIL
by overwriting the ASSIGNMENT FAIL with an ASSIGNMENT COMPL.

This patch fixes f_ass_patch_lcls() to only patch 'assignmentComplete'
members, if this assignmentComplete is actually chosen.

This fixes BSC_Tests.TC_assignment_fr_a5_1_codec_missing

Change-Id: I64fbf4cc3178a91913143960475a0d3758779ced
diff --git a/bsc/MSC_ConnectionHandler.ttcn b/bsc/MSC_ConnectionHandler.ttcn
index 225e86b..0846762 100644
--- a/bsc/MSC_ConnectionHandler.ttcn
+++ b/bsc/MSC_ConnectionHandler.ttcn
@@ -742,10 +742,12 @@
 	if (ispresent(g_pars.lcls.csc)) {
 		ass_tpl.pdu.bssmap.assignmentRequest.lCLS_ConnectionStatusControl := ts_BSSMAP_IE_LclsCsc(g_pars.lcls.csc);
 	}
-	if (ispresent(g_pars.lcls.exp_sts)) {
-		ass_cpl.pdu.bssmap.assignmentComplete.lCLS_BSS_Status := tr_BSSMAP_IE_LclsSts(g_pars.lcls.exp_sts);
-	} else {
-		ass_cpl.pdu.bssmap.assignmentComplete.lCLS_BSS_Status := omit;
+	if (ischosen(ass_cpl.pdu.bssmap.assignmentComplete)) {
+		if (ispresent(g_pars.lcls.exp_sts)) {
+			ass_cpl.pdu.bssmap.assignmentComplete.lCLS_BSS_Status := tr_BSSMAP_IE_LclsSts(g_pars.lcls.exp_sts);
+		} else {
+			ass_cpl.pdu.bssmap.assignmentComplete.lCLS_BSS_Status := omit;
+		}
 	}
 }