[processpool] handle BoJo case
[processpool] handle BoJo case

Summary:
Infer would crash when started in a context where it already had
children it didn't know about.

Reviewed By: martintrojer

Differential Revision: D19177589

fbshipit-source-id: 0c8831597

facebook/infer,jvillard/infer,facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer