libxl_migration: Resolve Coverity NULL_RETURNS
    
    Coverity noted that all callers to libxlDomainEventQueue() could ensure
    the second parameter (event) was true before calling except this case.
    As I look at the code and how events are used - it seems that prior to
    generating an event for the dom == NULL condition, the resume/suspend
    event should be queue'd after the virDomainSaveStatus() call which will
    goto cleanup and queue the saved event anyway.
    
    Signed-off-by: John Ferlan <jferlan@redhat.com>