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>
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