Pull Handler threw error but did not track it.

Somehow, I ended up with entries in `SourceControl.Git.DeploymentLog` where End Timestamp and Status are both blank:
```sql
SELECT *
FROM SourceControl_Git.DeploymentLog
WHERE EndTimestamp IS NULL
```

If a pull handler's `OnPull()` method ever throws an error, that information is not captured in the Deployment Log record, but it is returned and communicated back the call chain.

I do not know if this is related to #907 or not. Also, it is a little confusing that `ForModifications()` can return either the thrown exception OR the value of `%OnSave()`.