when temperature are negatives values are not corrects

indeed if negative temperature the hex value is of type 0xffe9 for
example giving a number > 65000, to deduct the negative value we need to
substract 0xffff to the hex value

ZgatewayBT.ino

@@ -322,6 +322,7 @@ boolean process_miflora_data(int offset, char * rest_data, char * mac_adress){
     break;
     case '4' :
           mactopic = mactopic + "/" + "tem";
+          if (value > 65000) value = value - 65535;
           dtostrf(value/10,3,1,val); // temp has to be divided by 10
     break;
     case '7' :