We're delaying any completed operation until we've completed an idle,
but the open/close state is changed and notified as soon as the device
completes the operation.
While this can be true, it means that we notify earlier than the finish
callback is actually called, while iterations are still needed to get
the actual state completed, and the current_task reset.
So if we'd open/close and iterate till fp_device_is_open() returns TRUE
we'd end up in a state in which the device is marked as ready, but it's
actually still busy since it's priv->current_task isn't unset yet.
The same if we'd try to do any action on notify::opened.
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