A police officer was accidently shot in the leg in a Staten Island precinct house last night, sources said. The unidentified cop was wounded shortly before midnight in the 120th Precinct station at 78 Richmond Terrace, sources said. It is believed the wounded officer was hit by a bullet from his own gun. The shooting happened before a shift change, when officers would be changing out of their gear. The cop only suffered a graze wound in his right calf.