unix: do not close invalid kqueue fd after fork
unix: do not close invalid kqueue fd after fork

The kqueue documentation states that the file descriptor is not
inherited by the child process. Hence, do not close it in uv_loop_fork
to avoid tampering with a possibly valid file descriptor already opened
by the child process.

PR-URL: https://github.com/libuv/libuv/pull/1583
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <838f779c91673db29b8572ea3f54d191d3878ae2@gmail.com>
Reviewed-By: Santiago Gimeno <3f17e29e343c4cf8809fb0970d81d6d8ee88d6b3@gmail.com>

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