Handle o2 voltage values < 0.5mV as invalid: Values < 0.5mv will now be handled as ppo2 = 0Bar to avaid problems (e.g. by negativ values) in the decompression calculation. In the custom display sensors with low voltage are show using '-'

Heinrichs Weikamp OSTC4 update files.

The builds are for testing purposes only. Be careful, they might not work and are definitely not recommended for real dives.