WASHINGTON — A network of secret prisons run by the former Syrian government is more extensive than the U.S. had realized, and is complicating efforts to find American journalist Austin Tice, the U.S. hostage envoy said Friday. The U.S. government initially estimated Syria had around 10 to 20 secret prisons, but there may be 40 or more, the chief envoy for hostage negotiations Roger Carstens told …