Return 0 from PollIoBackend::eb_event_add if the event type is not set
Return 0 from PollIoBackend::eb_event_add if the event type is not set

Summary: Return 0 from PollIoBackend::eb_event_add if the event type is not set

Reviewed By: danobi

Differential Revision: D21416811

fbshipit-source-id: 5825e473dca06d33017785e4d73947aade5f554c

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly