fix possible error on icecandidate event on RTCPeerConnection
fix possible error on icecandidate event on RTCPeerConnection

hit0907/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,hit0907/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,hit0907/cordova-plugin-iosrtc