JK BMS: fix SoC last update timestamp (#439)

for the MQTT integration, JkBms::DataPointContainer::updateFrom() was
changed such that the data points timestamp reflects the last change of
the data point value. that timestamp was used to set the SoC last update
timestamp. however, that timestampt must reflect the last time the SoC
was successfully received from the JK BMS so we could make sure the
value was up to date.

src/BatteryStats.cpp

@@ -180,12 +180,10 @@ void JkBmsBatteryStats::mqttPublish() const
 
 void JkBmsBatteryStats::updateFrom(JkBms::DataPointContainer const& dp)
 {
-    _dataPoints.updateFrom(dp);
-
     using Label = JkBms::DataPointLabel;
 
     _manufacturer = "JKBMS";
-    auto oProductId = _dataPoints.get<Label::ProductId>();
+    auto oProductId = dp.get<Label::ProductId>();
     if (oProductId.has_value()) {
         _manufacturer = oProductId->c_str();
         auto pos = oProductId->rfind("JK");
@@ -194,12 +192,14 @@ void JkBmsBatteryStats::updateFrom(JkBms::DataPointContainer const& dp)
         }
     }
 
-    auto oSoCValue = _dataPoints.get<Label::BatterySoCPercent>();
+    auto oSoCValue = dp.get<Label::BatterySoCPercent>();
     if (oSoCValue.has_value()) {
         _SoC = *oSoCValue;
-        auto oSoCDataPoint = _dataPoints.getDataPointFor<Label::BatterySoCPercent>();
+        auto oSoCDataPoint = dp.getDataPointFor<Label::BatterySoCPercent>();
         _lastUpdateSoC = oSoCDataPoint->getTimestamp();
     }
 
+    _dataPoints.updateFrom(dp);
+
     _lastUpdate = millis();
 }