(stable) Recover gracefully from Conduit failure when building "Tags" field in commit mail
Specifically, the issue is:
- We try to generate mail to a disabled user (later, we'll drop it without delivering it, but that filtering doesn't happen yet).
- The disabled user doesn't have permission to use Conduit (or any other Conduit-related problem occurs).
- We fail here, then retry generating the mail again later.
Instead, just degrade to not building the field and showing what went wrong.
- Pushed some commits, saw mail generate.
- Added a fake exception to the field, saw the mail generate with an error message.
Reviewed By: chad
Maniphest Tasks: T9458
Differential Revision: https://secure.phabricator.com/D14142