unregister request should be sent out only while registered

I noticed that while trigger the registration through cli cmd 'pjsip send register {arg}', the un-register request is sent regardless if it was registered or not.
This caused issues while it was not registered, the un-register request will fall into recovery or retry mechanism if the un-register request sent failed, and will keep try with expire=0 (un-register), hence no regular register could be sent out.