Events: fixed handling zero-length client address. On Linux recvmsg() syscall may return a zero-length client address when receiving a datagram from an unbound unix datagram socket. It is usually assumed that socket address has at least the sa_family member. Zero-length socket address caused buffer over-read in functions which receive socket address, for example ngx_sock_ntop(). Typically the over-read resulted in unexpected socket family followed by session close. Now a fake socket address is allocated instead of a zero-length client address.