Commit 0199955 ("fs: undo uv__req_init when uv__malloc failed")
mistakingly unregisters the requests unconditionally in a few places,
resulting in memory corruption when it hasn't been registered first.
Fixes: https://github.com/libuv/libuv/pull/543
PR-URL: https://github.com/libuv/libuv/pull/567
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>