fix reading time after date race

Author: ant32t

src/STM32RTC.cpp

@@ -1109,6 +1109,11 @@ time_t STM32RTC::getEpoch(uint32_t *subSeconds)
   syncDate();
   syncTime();
 
+  /* fix race condition where date may have changed between reading date and time */
+  if (_seconds == 0 && _minutes == 0 && _hours == 0) {
+    syncDate();
+  }
+
   tm.tm_isdst = -1;
   /*
    * mktime ignores the values supplied by the caller in the