QObject: Fix memory leak in queued_activate

queued_activate adds a reference to the slot object. It also attempts to
deref it again, but that did not work correctly so far. We could end up
with
T1                              |             T2
queued_activate                 |
  checks isSlotObject           |
    adds ref                    |
  locker.unlock()               |
                                | QObject::~QObject
                                |  //In disconnect all senders loop
                                |  sets isSlotObject to false
                                |  derefs slotObj, but not deleted
  checks isSlotObject           |
  (no deref because it's null)  |

To solve this issue and others caused by early returns, we now use a
RAII helper, which always takes care of calling destroyIfLastRef if the
ref count has been incremented.

Change-Id: I9c011cdb8faa5f344d7e70f024fc13f407e39ccf
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

0 files changed, 0 insertions, 0 deletions