sns: really reset readings on cfg reload

counter should start from scratch
amend 872f9b6

code/espurna/sensor.cpp

@@ -3867,9 +3867,12 @@ void configure_magnitude(Magnitude& magnitude) {
  magnitude.filter = magnitude::makeFilter(magnitude.filter_type);
  }
 
- // Some filters must be able store up to a certain amount of readings.
+ // Everything filtered so far is reset, possibly updating total number of required readings.
  magnitude.filter->resize(reportEvery());
 
+ // Reset internal readings counter as well.
+ magnitude.read_count = 0;
+
  // process emon-specific settings first. ensure that settings use global index and we access sensor with the local one
  if (isEmon(magnitude.sensor) && magnitude::traits::ratio_supported(magnitude.type)) {
  auto* sensor = static_cast<BaseEmonSensor*>(magnitude.sensor.get());