R1:3b2868e15553

Fix searching legalpad documents by contributors

Summary:
Found in a change submitted to Phorge (https://we.phorge.it/D25018#inline-231), this fixes a typo in populating search the `contributorPHIDs` constraint in the Legalpad search engine.

Currently when trying to search legalpad documents by contributor an error is encountered:
```lang=console
Array for %Ls conversion is empty. Query: contributor.dst IN (%Ls)
```

Test Plan: I searched for legalpad documents based on a contributor and got back correct…