On my system, when trying to use mpv with a read-only fd created by python 3.7, `send` triggers ENOTSOCK, not EBADF. Extend the logic to detect non-writable fds by this `errno`.
On my system, when trying to use mpv with a read-only fd created by python 3.7, `send` triggers ENOTSOCK, not EBADF. Extend the logic to detect non-writable fds by this `errno`.