bugfix: User.__init__ was only handling the case where full_name or first_name was an empty string, but not None
bugfix: User.__init__ was only handling the case where full_name or first_name was an empty string, but not None

Actually inserting a User with full_name or first_name of None into the UserList would cause errors in utils.get_conv_name()

tdryer/hangups,ddboline/hangups,das7pad/hangups