Avoid a resource leak

It seems an aged mistake to pass pUnoCrsr to a std::auto_ptr too early

Change-Id: I99ab2d8c8719fb9f0fc3e90f36534007b4cde990
Reviewed-on: https://gerrit.libreoffice.org/8393
Tested-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>