Properly use critical section

The critical section was not actually protecting the variable as it is read, but could change prior to the critical section start.
With this change, the variable is read and reset inside the critical section in order to make this atomic and not miss any events.

Author: daltonate

src/mac/LoRaMac.c

@@ -1351,13 +1351,15 @@ static void ProcessRadioRxTimeout( void )
 
 static void LoRaMacHandleIrqEvents( void )
 {
-    LoRaMacRadioEvents_t events = LoRaMacRadioEvents;
+    LoRaMacRadioEvents_t events;
+
+    CRITICAL_SECTION_BEGIN( );
+    events = LoRaMacRadioEvents;
+    LoRaMacRadioEvents.Value = 0;
+    CRITICAL_SECTION_END( );
+
     if( events.Value != 0 )
     {
-        CRITICAL_SECTION_BEGIN( );
-        LoRaMacRadioEvents.Value = 0;
-        CRITICAL_SECTION_END( );
-
         if( events.Events.TxDone == 1 )
         {
             ProcessRadioTxDone( );