Update last attempt only if RTC is online

Re-implementing main #422 - 09a4b45

Author: nseidle

Firmware/RTK_Everywhere/MQTT_Client.ino

@@ -463,9 +463,10 @@ void mqttClientReceiveMessage(int messageSize)
                 settings.pointPerfectNextKeyDuration =
                     (1000LL * 60 * 60 * 24 * 28) - 1; // Assume next key duration is 28 days
 
-                settings.lastKeyAttempt = rtc.getEpoch(); // Mark it
-                
-                recordSystemSettings();                   // Record these settings to unit
+                if (online.rtc)
+                    settings.lastKeyAttempt = rtc.getEpoch(); // Mark it - but only if RTC is online
+                    
+                recordSystemSettings();                       // Record these settings to unit
 
                 if (settings.debugCorrections == true)
                     pointperfectPrintKeyInformation();