correct double variable declaration and use arduino json implicit cast

OpenMQTTGateway.ino

@@ -830,22 +830,22 @@ void receivingMQTT(char * topicOri, char * datacallback) {
   if (strstr(topicOri, subjectMultiGTWKey) != NULL) // storing received value so as to avoid publishing this value if it has been already sent by this or another OpenMQTTGateway
   {
     trc(F("Storing signal"));
+    unsigned long data = 0;
     #ifdef jsonPublishing
-    trc(F("Creating Json buffer"));
-    StaticJsonBuffer<JSON_MSG_BUFFER> jsonBuffer;
-    JsonObject& jsondata = jsonBuffer.parseObject(datacallback);
-    unsigned long data = strtoul(jsondata["value"], NULL, 10); // we will not be able to pass values > 4294967295
-    storeValue(data);
-    trc(F("Data from JSON stored"));
+      trc(F("Creating Json buffer"));
+      StaticJsonBuffer<JSON_MSG_BUFFER> jsonBuffer;
+      JsonObject& jsondata = jsonBuffer.parseObject(datacallback);
+      if (jsondata.success())  data =  jsondata["value"];
     #endif
 
-   
     #ifdef simplePublishing
-    unsigned long data = strtoul(datacallback, NULL, 10); // we will not be able to pass values > 4294967295
-    storeValue(data);
-    trc(F("Data stored"));
+      data = strtoul(datacallback, NULL, 10); // we will not be able to pass values > 4294967295
     #endif
     
+    if (data != 0) {
+      storeValue(data);
+      trc(F("Data from JSON stored"));
+    }
   }
   //YELLOW ON
   digitalWrite(led_send, LOW);