library: Ensure setverdict(fail) is followed by mtc.stop

This will prevent subsequent failures from overwriting the verdict so we
can easily see the root cause of the test failure.

Using testcase.stop instead for errors internal to our test
infrastructure to mark them as test errors instead of failed.

Change-Id: Idc6819aaf0b01e70c38fad828dd44dcec6bdd778
diff --git a/library/MNCC_Types.ttcn b/library/MNCC_Types.ttcn
index 19af236..157457a 100644
--- a/library/MNCC_Types.ttcn
+++ b/library/MNCC_Types.ttcn
@@ -1922,7 +1922,7 @@
 		return pdu.u.signal.callref;
 	} else  {
 		setverdict(fail, "Unable to determine Callref for MNCC", pdu);
-		self.stop
+		mtc.stop
 	}
 }