face: Reset io_service after io_service::poll()

In the case when after the io_service::poll call from the inside of
processEvents(<negative time>) there are no more handlers to dispatch,
io_service is moved to "stopped" state, which requires
io_service::reset() to be called in order for the future events to be
dispatched in subsequent poll/processEvents call.

Change-Id: I3dd4c44550a5cf6c6885f249ccfb7ba2fbf8198d