Segfault fix + small improvement 

Upon the connection error only a simple message is printed via the qDebug thingy. However, I don't know if running this application without the D-Bus connection is reasonable after all. Anyway, I think it's better then nasty segfault.

Nice app btw. It would be nice to have some kind of exclude list for "on-board" devices.

Cheers,
Arek