Specifically return success. It fixes a tight loop on unices as `sendfile()` was returning 0 and also makes the function behave the same both on `unix` and `windows`. It partially implements: https://github.com/libuv/libuv/issues/2237 PR-URL: https://github.com/libuv/libuv/pull/2298 Refs: https://github.com/nodejs/node/issues/27746 Reviewed-By: Jameson Nash <vtjnash@gmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com>