QDBusConnection::connectToBus fails dbus API check when q_dbus_bus_register fails

When the connection is established but the registration fails (for example the maximum number of connections was reached) QtDBus calls q_dbus_connection_unref without calling q_dbus_connection_close if the connection is connected.

This will trigger the following failed check in dbus (dbus-connection.c:2792).

"The last reference on a connection was dropped without closing the connection. This is a bug in an application. See dbus_connection_unref() documentation for details."