As of 4f294a90, a SmTextNode can be
the sole child of a SmLineNode without being wrapped in a SmExpressionNode.

Change-Id: I3779eb90e216a70566c1151a9b8cb91a9fa36519
Reviewed-on: https://gerrit.libreoffice.org/17613Reviewed-by: Regina Henschel <rb.henschel@t-online.de>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>