1. Fixed bug whereby B2 press could make liquid shoot out when cylinder was off, gas line removed from keg, but liquid-out line was connected. Now, we trap user in null pressure loop until pressure is fixed, only allowing B2 open and close door.
1. Added startPressure > nullPressure condition in Fill Loop to prevent condition where B2 can start spewing if 1) CO2 off, 2) keg pressurized, 3) gas line disconnected and liquid line connected.
2. Added some button beeps in null loop.