Add error handling for dbus errors in dbus-call-with-callback.

This was the reason why m_recreateBusy could be stuck to 'true' forever,
the normal callback wasn't called because the DBus call ended in error
(my guess is a timeout due to extra-busy system, or kbuildsycoca crashing).

Old bug, first reported in 2008...


FIXED-IN: 4.13