getCellularTime return UNIX epoch if NTP sync fails

Author: pennam

Diff for: src/ArduinoCellular.cpp

@@ -122,10 +122,16 @@ Time ArduinoCellular::getGPSTime(){
 }
 
 Time ArduinoCellular::getCellularTime(){
-    int year, month, day, hour, minute, second;
+    int year = 1970;
+    int month = 1;
+    int day = 1;
+    int hour = 0;
+    int minute = 0;
+    int second = 0;
     float tz;
-    modem.NTPServerSync();
-    modem.getNetworkTime(&year, &month, &day, &hour, &minute, &second, &tz);
+    if (modem.NTPServerSync() != -1) {
+      modem.getNetworkTime(&year, &month, &day, &hour, &minute, &second, &tz);
+    }
     return Time(year, month, day, hour, minute, second);
 }