Trap for trivial sectors in Altitude AAL

alt_idxs += quick.start or 0
can fail if sector does not exceed 500ft. e.g.
list(speedies)
[Section(name='Fast', slice=slice(644, 2710, None), start_edge=644,
stop_edge=2710), Section(name='Fast', slice=slice(2711, 2713, None),
start_edge=2711, stop_edge=2713)]