Check if the pipe array is empty before calling stream_select()
bug #9367 [Process] Check if the pipe array is empty before calling stream_select() (jfposton)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #9367).

Discussion
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[Process] Check if the pipe array is empty before calling stream_select()

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9280
| License       | MIT
| Doc PR        |

ProcessPipes generates a warning frequently which can cause issues for custom shutdown functions. Adding a check to see if the pipe array is empty should be functionally equivalent without having to generate the error.

Fixes: #9280

Commits
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12f95e2 [Process] Check if the pipe array is empty before calling stream_select()