DataOffer not invalidated when client loses keyboard focus

According to wayland doc:
A.10.2.6. wl_data_device::selection - advertise new selection
The selection event is sent out to notify the client of a new wl_data_offer for the selection for this device. The data_device.data_offer and the data_offer.offer events are sent out immediately before this event to introduce the data offer object. The selection event is sent to a client immediately before receiving keyboard focus and when a new selection is set while the client has keyboard focus. The data_offer is valid until a new data_offer or NULL is received or until the client loses keyboard focus.

The data_offer object should be invalidated when client loses keyboard focus. Otherwise in following scenario, it will become zombie object:
start app1 -> copy text -> start app2 -> paste text -> close app1 -> paste again in app2 -> seg fault in qtwayland.

The root cause is that when app2 takes focus the first time, data_device.data_offer event was sent to it in DataDevice::setFocus. When app1 is closed, the data source reference in data offer becomes invalid. so when trying to paste again in app2, segmentation faults