Do not raise an exception when UA is closed
Do not raise an exception when UA is closed

.. and a UA method is executed

tqcenglish/JsSIP,CodeYellowBV/JsSIP,rusekr/JsSIP,Escaux/SIP.js,Voiceworks/SIP.js,josephfrazier/SIP.js,onsip/SIP.js,markandrus/SIP.js,onsip/SIP.js,dpocock/JsSIP,ronlobo/SIP.js,AaronZhangL/JsSIP,voxbone/JsSIP,joseph-onsip/SIP.js,vconsult/JsSIP,DrumTechnologiesLtd/JsSIP