Fix Qt::QueuedConnection when signal has a return value

Fix Qt::QueuedConnection when signal has a return value

For queued connections, the args[0] is set to null as it make no sens to
forward the return value to the signal.
So we need to check in the operator, that the pointer is not null.
(container.data is args[0])

Change-Id: I80bde66f1ec19de0f4962c80e5b2797d2819075c
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>