Debugger: Fix threadname display

We probably should completely skip the code in the cases where Qt
itself already propagates the object name to the underlying threads.

Task-number: QTCREATORBUG-10826
Change-Id: I7e9e5b7c990a270c8563e40c1fe1e900724c1e5c
Reviewed-by: Ryan May <ryan.may@eecradar.com>
Reviewed-by: hjk <hjk121@nokiamail.com>