Check NULL pointer input for vEventGroupDelete. (#293)

* Check NULL pointer input for vEventGroupDelete.

* Change the input parameter check with assertion.

Co-authored-by: Cobus van Eeden <35851496+cobusve@users.noreply.github.com>

event_groups.c

@@ -625,6 +625,8 @@ EventBits_t xEventGroupSetBits( EventGroupHandle_t xEventGroup,
 
 void vEventGroupDelete( EventGroupHandle_t xEventGroup )
 {
+    configASSERT( xEventGroup );
+
     EventGroup_t * pxEventBits = xEventGroup;
     const List_t * pxTasksWaitingForBits = &( pxEventBits->xTasksWaitingForBits );