Changing the constructor of the CreateImpromptuMUCUIEvent class not to accept default values to its parameters. This approach is less prone to mistakes, like forgetting an argument. This commit fixes SWIFT-271 bug, where only two arguments were being passed in the constructor. As a result the reason string was used to create a room JID, making the room unusable. By passing an empty string, the room JID created is not valid, and when ChatsManager handles the event, it will generate a new valid room JID. Test information: Unit test pass. Tested the creation of new impromptu chat with with windows 10 (qt5.7). Change-Id: I4ce9ee7db14b9125970a03f19d1ac0c32e1b5a0e