fix bug in selector drop

src/sys/windows/named_pipe.rs

@@ -942,7 +942,10 @@ fn event_done(status: &OVERLAPPED_ENTRY, events: Option<&mut Vec<Event>>) {
     let io = me.io.lock().unwrap();
 
     // Make sure the I/O handle is still registered with the selector
-    if io.token.is_some() {
+    //
+    // This method is also called during `Selector::drop` to perform cleanup. In
+    // this case, `events` is `None` and we don't need to track the event.
+    if io.token.is_some() && events.is_some() {
         let mut ev = Event::from_completion_status(&status);
         // Reverse the `.data` alteration done in `schedule_event`. This
         // alteration was done so the selector recognized the event as one from