An oversupply of flats threatens to lower Singapore’s property prices, the city state’s central bank has warned.The number of unsold units from new projects doubled to 4,377 in the third quarter, the Monetary Authority of Singapore (MAS) said in its annual Financial Stability Review released on Thursday.The overhang will probably “be exacerbated in the medium term” as developers launch projects from a series of redevelopment or “en bloc” deals struck in the past two years, MAS said.In wealthy…