VM eventhandler: Update epoll/kqueue even if the only event is an error

runtime/bin/eventhandler_macos.cc

Index: runtime/bin/eventhandler_macos.cc
diff --git a/runtime/bin/eventhandler_macos.cc b/runtime/bin/eventhandler_macos.cc
index ea0d5dabb2866648ba9f10732d388bf5dfaf65fc..7aa9280b2f58aae8efa5c8753e2fdfc9235e495d 100644
--- a/runtime/bin/eventhandler_macos.cc
+++ b/runtime/bin/eventhandler_macos.cc
@@ -389,13 +389,11 @@ void EventHandlerImplementation::HandleEvents(struct kevent* events, int size) {
     } else {
       DescriptorInfo* di = reinterpret_cast<DescriptorInfo*>(events[i].udata);
       const intptr_t old_mask = di->Mask();
-      intptr_t event_mask = GetEvents(events + i, di);
+      const intptr_t event_mask = GetEvents(events + i, di);
       if ((event_mask & (1 << kErrorEvent)) != 0) {
         di->NotifyAllDartPorts(event_mask);
-      }
-      event_mask &= ~(1 << kErrorEvent);
-
-      if (event_mask != 0) {
+        UpdateKQueueInstance(old_mask, di);
+      } else if (event_mask != 0) {
         Dart_Port port = di->NextNotifyDartPort(event_mask);
         ASSERT(port != 0);
         UpdateKQueueInstance(old_mask, di);