altos: full logging must flush pending data before checking state

Flight state must be checked only after any pending data have been
written to the log as the 'current' flight state is only valid when
the pending data values have been processed. This ensures that the
'boost' state is not marked until the full ring of data is
written. This ensures that the data processing code can find the
barometer values from before boost to get an idea of the ground
pressure value.

Signed-off-by: Keith Packard <keithp@keithp.com>