Update LoRaMac-node to Version 4.4.4，fix Security breach found by Tencent Blade Team please refer to security advisory - CVE-2020-11068

fix Security breach found by Tencent Blade Team please refer to security advisory - CVE-2020-11068

components/connectivity/LoraWAN/system/timer.c

@@ -351,6 +351,10 @@ TimerTime_t TimerGetCurrentTime( void )
 
 TimerTime_t TimerGetElapsedTime( TimerTime_t past )
 {
+    if ( past == 0 )
+    {
+        return 0;
+    }
     uint32_t nowInTicks = RtcGetTimerValue( );
     uint32_t pastInTicks = RtcMs2Tick( past );