fix --disable-lpsolve build: wrong condition for 'solver' library

Change-Id: I31c4ac127e8092ffb854f57efa5fb7226f229a35
Reviewed-on: https://gerrit.libreoffice.org/9305
Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>