Only set time when NTP didn't run

ampel-firmware/util.cpp

@@ -32,13 +32,14 @@ String macToID() {
 namespace ntp {
   WiFiUDP ntpUDP;
   NTPClient timeClient(ntpUDP, config::ntp_server, config::utc_offset_in_seconds, 60000UL);
+  bool connected_at_least_once = false;
 
   void initialize() {
     timeClient.begin();
   }
 
   void update() {
-    timeClient.update();
+    connected_at_least_once |= timeClient.update();
   }
 
   void getLocalTime(char *timestamp) {
@@ -50,6 +51,9 @@ namespace ntp {
     timeClient.getFormattedDate(time);
     Serial.print(F("Current time : "));
     Serial.println(time);
+    if (connected_at_least_once) {
+      Serial.println(F("NTP update already happened. Not changing anything."));
+    }
     Serial.print(F("Setting UNIX time to : "));
     Serial.println(unix_seconds);
     timeClient.setEpochTime(unix_seconds - seconds());