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

runtime/bin/eventhandler_linux.cc

Index: runtime/bin/eventhandler_linux.cc
diff --git a/runtime/bin/eventhandler_linux.cc b/runtime/bin/eventhandler_linux.cc
index ea62bd5b1a4cd47c0521384812f3cf3ae37f6ccc..24e7755bd68aaa51894a97745d6db2b5e0be2a2f 100644
--- a/runtime/bin/eventhandler_linux.cc
+++ b/runtime/bin/eventhandler_linux.cc
@@ -362,13 +362,11 @@ void EventHandlerImplementation::HandleEvents(struct epoll_event* events,
       DescriptorInfo* di =
           reinterpret_cast<DescriptorInfo*>(events[i].data.ptr);
       const intptr_t old_mask = di->Mask();
-      intptr_t event_mask = GetPollEvents(events[i].events, di);
+      const intptr_t event_mask = GetPollEvents(events[i].events, di);
       if ((event_mask & (1 << kErrorEvent)) != 0) {
         di->NotifyAllDartPorts(event_mask);
-      }
-      event_mask &= ~(1 << kErrorEvent);
-
-      if (event_mask != 0) {
+        UpdateEpollInstance(old_mask, di);
+      } else if (event_mask != 0) {
         Dart_Port port = di->NextNotifyDartPort(event_mask);
         ASSERT(port != 0);
         UpdateEpollInstance(old_mask, di);