Dexcom sensor error displays as zero, instead of as stale data

[phelpy]

Background: Dexcom has recently updated their app so that a sensor error will display in the dexcom app as a “—-“ and as a “0” on the dexcom graph. This makes the glance app display a “0” and give warnings for low blood sugar instead of for stale data.

Request: Update glance so that a sensor error in dexcom is correctly
treated as stale data in glance.

Secondary Request: Have the sensor error displays as a something other than “0”.