The ... idiomatic C++ code in TVChildTarget::Check() and
SearchAndInsert() handles ownership in non-obvious ways,
so it's not surprising that it took offense at the recent
conversion to std::unique_ptr.  Let's at least try to
prevent it from crashing so quickly.

(regression from 4b69497e)

(cherry picked from commit 8a3bb935)

Attempt to blind fix build breaker
(cherry picked from commit 4094f9ba)

Change-Id: I0981707a61aee1733e727b1c00346d8ec524362e
Reviewed-on: https://gerrit.libreoffice.org/46376Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>