Access log: fix default value, broken by cb308813b453. log->filter ("if" parameter) was uninitialized when the default value was being used, which would lead to a crash (SIGSEGV) when access_log directive wasn't specified in the configuration. Zero-fill the whole structure instead of zeroing fields one-by-one in order to prevent similar issues in the future. Signed-off-by: Piotr Sikora <piotr@cloudflare.com>