Don't spill an extra pick from old node breakers

Don't spill an extra pick from old node breakers

Due to historical shenanigans around the addition of the pick slot to
node breakers, some breakers that were placed before the addition have
ended up with a mese pick in their newly-acquired pick slot, rather than
in the ghost_pick slot where it belongs.  This causes these breakers to
spill this ghost pick when they are broken.  To avoid this, make pick
spilling conditional on the breaker having a formspec: pre-slot breakers
don't have one.