A maniac slashed a man and a woman in separate attacks in the Grand Central-42nd Street Station on Christmas Eve, according to cops and law enforcement sources.The assailant first knifed a 42-year-old man across the left wrist after the two got into an argument on the stairs of the southbound entrance of the Midtown station around 10:15 p.m., police and the sources said.The suspect then ran up some stairs and got into an argument with the woman, 26, before slashing her on the neck near a turnstile, according to sources.Both victims were taken to Bellevue Hospital in stable condition.Following the second slashing, the suspect fled up an escalator, but witnesses got the attention of cops who arrested him and recovered a knife, sources said.The NYPD said the department has a person of interest in custody.No charges have been filed yet.The suspect has three prior arrests for criminal mischief, fare beating, and assaulting a police officer, according to sources....