Honolulu City Councilwoman Carol Fukunaga wants all vacant city-owned affordable housing units rented.   Some of the 236 units in the Marin Tower on North Nimitz Highway are empty but are being maintained with taxpayer money. There are other buildings with empty units being mantained on the taxpayer's dime. But Fukunaga says the city should allow those in the middle-income range who are eligible, to rent the units. She said those people would have more money to spend in Chinatown stores. Fukunaga said her plan won't displace low income renters who live in the Chinatown buildings. It would add tenants who have a little more money, and fill a void that's costing taxpayers money.