TRUNK-4565: Avoid a null pointer exception when validating Stop Orders for DrugOrder...

...s without a Drug.


It is valid to have a DrugOrder without a Drug, as long as there is a Concept.  The logic on lines 184-192 addresses that case.  However, line 179 was throwing NPE's when trying to stop a DrugOrder without a Drug.

See issue here https://issues.openmrs.org/browse/TRUNK-4565