call propertyHiddenChanged synchronously

[simonschmeisser]

Property might no longer exist when event is triggered

fixes #1657

[rhaschke]

I'm not sure why a queued connection was used here. But instead of changing the connection type (which might have other side effects), what about changing the argument from Property* to QPointer<Property>?
This way, we would notice any invalidation of the held Property and you could easily check this in PropertyTreeWidget::propertyHiddenChanged.

[simonschmeisser]

I'll test QPointer as well, didn't have it in my mind.

[simonschmeisser]

I didn't observe any difference between the QueuedConnection variant with QPointer and the synchronous version with the raw pointer.

Git blame does not give any reason as to why this is queued, it was added in the context of initially implementing point cloud displays.

[rhaschke]

Thanks for implementing the QPointer variant too. Thanks, also, for checking git history. Indeed, the queue connection was introduced as part of 3bbf90e. Given that, the QPointer approach requires API /ABI changes, I validated that a direct connection doesn't harm showing/hiding properties of PCD. I think I will merge your initial solution then. I'm sorry for the extra work.

[rhaschke]

@simonschmeisser, could you please revert the 2nd commit? Thanks.