HTTP+JSON power meter: value 1 is always enabled

enabling the HTTP+JSON power meter without enabling at least one value
makes no sense, so value 1 has always been treated as "always enabled".
while doing the power meter refactoring, however, a regression was
introduced that would hide the settings for value 1 in the web UI until
the power meter settings would be saved, which they cannot be due to
missing settings for value 1.

src/Configuration.cpp

@@ -338,6 +338,8 @@ void ConfigurationClass::deserializePowerMeterHttpJsonConfig(JsonObject const& s
         t.PowerUnit = s["unit"] | PowerMeterHttpJsonValue::Unit::Watts;
         t.SignInverted = s["sign_inverted"] | false;
     }
+
+    target.Values[0].Enabled = true;
 }
 
 void ConfigurationClass::deserializePowerMeterHttpSmlConfig(JsonObject const& source, PowerMeterHttpSmlConfig& target)

src/WebApi_powermeter.cpp

@@ -160,7 +160,6 @@ void WebApiPowerMeterClass::onAdminPost(AsyncWebServerRequest* request)
 
     Configuration.deserializePowerMeterHttpJsonConfig(root["http_json"].as<JsonObject>(),
             config.PowerMeter.HttpJson);
-    config.PowerMeter.HttpJson.Values[0].Enabled = true;
 
     Configuration.deserializePowerMeterHttpSmlConfig(root["http_sml"].as<JsonObject>(),
             config.PowerMeter.HttpSml);

webapp/src/views/PowerMeterAdminView.vue

@@ -144,7 +144,7 @@
                             v-model="httpJson.enabled"
                             type="checkbox" wide />
 
-                        <div v-if="httpJson.enabled">
+                        <div v-if="httpJson.enabled || index == 0">
 
                             <HttpRequestSettings v-model="httpJson.http_request" v-if="index == 0 || powerMeterConfigList.http_json.individual_requests"/>