Move code that dereferences ConnectionPort into the if(ConnectionPort) block

The old code that dereferences ConnectionPort after if (ConnectionPort)

This might not be a problem, since it depends on a condition that is probably never true when ConnectionPort is NULL, but it should probably still not be done on that path.
It might as well be done further down, but doing it before ObDereferenceObject(ConnectionPort) seems to make sense.
This is an old patch by Samuel.