vdagent-x11: Listen for selection owner window destroy / close events too
vdagent-x11: Listen for selection owner window destroy / close events too

These rarely happen as most apps have the decency to do a SetSelectionOwner
None before exiting. But some do not, so listen for these too.

elmarco/vdagent-gtk,elmarco/vdagent-gtk,elmarco/vdagent-gtk