Commit c24b7a7e reworked the way lookahead was done and it introduced
a bug when a full acceleration move is immiedietly followed by a full
deceleration move. In that situation, depending on when the lookahead
queue was flushed, it was possible to call move.move() without calling
move.set_junction(). This resulted in a "Move instance has no
attribute 'accel_t'" internal error.
Simplify and fix the logic for checking full accel moves followed by
full decel moves.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>