Fix selection handling for invalid dives

This is the downside of having to track our own selection state. We now
have a class of dives that potentially isn't known to Gtk as we aren't
adding them to the TreeView. So we need to make sure that their selection
state is consistent by deselecting them (either when they are marked as
invalid OR when we change preferences to no longer show invalid dives).

And because Gtk sends out another set of selection events when clearing
the TreeView (not sure why), we also need to make sure that their
selection state isn't reset to selected by mistake when the divelist is
recreated.

A bit of a pain, but it seems to work now and be consistent.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>