A private developer’s proposal to convert empty buildings near the Dirksen Federal Courthouse into apartments worries Chief U.S. District Judge Ruben Castillo.“Courthouse security for me as chief judge is a top priority,” Castillo said Thursday in his annual State of the Court address.And he said the proposed project involving a row of buildings in the 200 block of South State Street raises safety concerns.One of the buildings would be turned into micro-apartments housing a “very transient, unstable …