fix PluginRTCPeerConnectionConstraints:parseConstraints crash on optional peer constraints
fix PluginRTCPeerConnectionConstraints:parseConstraints crash on optional peer constraints

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