[Process][2.2] Close unix pipes before calling `proc_close` to avoid a deadlock

| Q             | A
| ------------- | ---
| Bug fix?      | potentially
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT

see http://php.net/manual/en/function.proc-close.php