"Next reading" values broken

[linus-ha]

When starting ddguard at the time when no sensor is connected, the received values for "sensorBGL:" and "sensorBGLTimestamp" are 0, so that the next reading will be scheduled for the 01.01.1970 at 01:05 which will never be reached.

[...]
### BGL ###
sensorBGL:                0
sensorBGLTimestamp:       1970-01-01 01:00:00+01:00
trendArrow:               -3

account for pump RTC drift:
   before: pumpTime 2021-01-02 21:29:47.999971+01:00,  sensorBGLTimestamp 1970-01-01 01:00:00+01:00
   after : pumpTime 2021-01-02 21:28:22.652260+01:00,  sensorBGLTimestamp 1970-01-01 01:00:00+01:00
Uploading data to Nightscout
Sensor lost, not uploading SGV data
Next reading at 1970-01-01 01:05:00+01:00, -1609619005 seconds from now