[2.3] [Process] Use correct test for empty string in UnixPipes

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

This PR supersedes #11264 : 2.3 compatibility + Windows compatibility + CS fix
Here we need a command that only prints `0`. `echo` adds a new line on both systems, it prints `0\n` on linux and `0\r\n` on windows. Unfortunately, AFAIK there is no equivalent of bash `printf` command on windows.