Fixes T9631. Build steps created before I added this option may not have it specified, which could throw later. Make handling a little more robust.
- Maniphest Tasks
- T9631: Don't crash when users fail to specify additional working copies
- Restricted Diffusion Commit
rP43569d4e278c: Make WorkingCopy build step slightly more durable
Will ask @yelirekim to report back.