Code review comment for lp:~nick-dedekind/qtmir/lp1475678.surface-occlude

MirSurface should call deleteLater() if the last MirSurfaceItem unregisters from it and it's no longer live() or pointed to by a session.

Ie, this code should be kept:

"""
if (m_viewCount == 0) {
    [..]
    if (m_session.isNull() || !m_live) {
        deleteLater();
    }
}
"""