When only a dive trip is selected, select all the dives in the trip

This does a final pass after all the selection logic, and notices if we
have dive trips that are selected, but that have no dives in them
selected.  In that case, we assume that the user wanted to select all
dives in that trip.

NOTE! This still allows a range selection that selects the dive trip
entry and a few dives under the trip.  If a trip has any dives selected
in it, we leave that manual selection alone.  So this new logic really
only triggers on the case where somebody selected *just* the trip.

Note: unselecting the trip still leaves the dives under it selected,
because having a dive trip that isn't selected have all the dives under
it be selected is normal, and we can't recognize that as some kind of
special event.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>