CLOUDSTACK-3485: NPE while getting instance ID from Asyn Job when

publishing async job events on eventbus

handing case where instance id is null in the asyn job, while publishing
asyn job events on to event bus

server/src/com/cloud/api/ApiDBUtils.java

@@ -1279,9 +1279,11 @@ public class ApiDBUtils {
     }
 
     public static String findJobInstanceUuid(AsyncJob job){
-        if ( job == null )
+        if ( job == null || job.getInstanceId() == null)
             return null;
+
         String jobInstanceId = null;
+
         if (job.getInstanceType() == AsyncJob.Type.Volume) {
             VolumeVO volume = ApiDBUtils.findVolumeById(job.getInstanceId());
             if (volume != null) {