Fix #78210: Invalid pointer address

Fix #78210: Invalid pointer address

This is actually about three distinct issues:

* If an empty string is passed as $address to `stream_socket_sendto()`,
  the `sa` is not initialized, so we must not pass it as `addr` to
  `php_stream_xport_sendto()`.

* On POSIX, `recvfrom()` truncates messages which are too long to fit
  into the specified buffer (unless `MSG_PEEK` is given), discards the
  excessive bytes, and returns the buffer length.  On Windows, the same
  happens, but `recvfrom()` returns `SOCKET_ERROR` with the error code
  `WSAEMSGSIZE`.  We have to catch this for best POSIX compatibility.

* In `php_network_parse_network_address_with_port()`, we have to zero
  `in6` (not only its alias `sa`) to properly support IPv6.

Co-Authored-By: Nikita Popov <nikita.ppv@googlemail.com>