Add call observer only when matrix sesion is running. The call observer is removed in other session states.
Add call observer only when matrix sesion is running. The call observer is removed in other session states.

vector-im/vector-ios,vector-im/riot-ios,vector-im/riot-ios,matrix-org/matrix-ios-console,vector-im/riot-ios,vector-im/vector-ios,vector-im/riot-ios,vector-im/vector-ios,vector-im/riot-ios,matrix-org/matrix-ios-console,vector-im/riot-ios