qemu: Reset hasManagedSave after removing a corrupted image
    
    When starting a domain with managed save image, we try to restore it
    first. If the image is corrupted, we silently unlink it and just
    normally start the domain. At this point the domain has no managed save
    image, yet we did not reset the hasManagedSave flag.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1460962
    
    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>