Shortly before the start of the criminal trial of former Volkswagen chief Martin Winterkorn, the health condition of the former top executive at the German carmaking giant has deteriorated once again. The 77-year-old had to undergo another knee surgery following a medical emergency, sources close to him confirmed to dpa. The surgery went well, but Winterkorn remains physically very weakened. He is currently being treated in a rehab clinic. The criminal trial of the former VW Group chief executive relating to the diesel scandal is set to begin at the Regional Court of Braunschweig in northern G…