So far, for some (?) errors, `uv_try_write()` returns `EAGAIN`
regardless of the actual error, so `ECONNRESET` and `EPIPE` errors
can be swallowed here.
This commit changes `uv_try_write()` so that it prefers to return
the actual error it has seen.
PR-URL: https://github.com/libuv/libuv/pull/2321
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
