R1:27ce69183900

Fix an issue with the Herald engine field value cache

Summary:
To improve the performance of Herald, we attempt to generate the value for each field (e.g., a task title) only once.

For most field values this is cheap, but for some (like a commit's branches) it can be quite expensive. We only want to pay this cost once, so we cache field values.

However, D12957 accidentally added a check where we bypass the cache and generate the value for every field, before reading the cache. This causes us to generate…