A hidden safe that was discovered during the renovation of the former Bill's Lake Tahoe Casino building last month has been opened, but the Oprah Winfrey Network has the right to release what was found.A Douglas County Sheriff's Office investigator was present at the opening of the safe Wednesday, but did not find anything relevant to an investigation, wrote Sgt. Jim Halsey in an email."Nothing of substance for us inside, and the contents are being kept a secret until the Oprah Winfrey show airs in a month or so," Halsey wrote.The footage of the safe being opened will be used …