Rather than asserting that a tor network never has more than 253 authorities, we could instead log when we truncate the number of reveals in the shared random hash. As a consequential change, we should do this truncation as late as possible, so that the value assigned to `srv->num_reveals` is not truncated. In any case, `tor_assert(reveal_num < UINT8_MAX);` is unnecessarily strict, it can be `tor_assert(reveal_num <= UINT8_MAX);`. Please see my branch sr-no-crash on https://github.com/teor2345/tor.git for fixes to these issues.