configure.ag: do not overwrite default when --with-hts is not provided
configure.ag: do not overwrite default when --with-hts is not provided

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb