Re: [PATCH 1/3] builtin/backfill: fix flags passed to `odb_has_object()`

> The function `fill_missing_blobs()` receives an array of object IDs and
> verifies for each of them whether the corresponding object exists. If it
> doesn't exist, we add it to a set of objects and then batch-fetch all of
> the objects at once.
> 
> The check for whether or not we already have the object is broken
> though: we pass `OBJECT_INFO_FOR_PREFETCH`, but `odb_has_object()`
> expects us to pass `HAS_OBJECT_*` flags. The flag expands to:
> 
>   - `OBJECT_INFO_QUICK`, which asks the object database to not reprepare
>     in case the object wasn't found. This makes sense, as we'd otherwise
>     reprepare the object database as many times as we have missing
>     objects.
> 
>   - `OBJECT_INFO_SKIP_FETCH_OBJECT`, which asks the object database to
>     not fetch the object in case it's missing. Again, this makes sense,
>     as we want to batch-fetch the objects.
> 
> This shows that we indeed want the equivalent of this flag, but of
> course represented as `HAS_OBJECT_*` flags.
> 
> Luckily, the code is already working correctly. The `OBJECT_INFO` flag
> expands to `(1 << 3) | (1 << 4)`, none of which are valid `HAS_OBJECT`
> flags. And if no flags are passed, `odb_has_object()` ends up calling
> `odb_read_object_info_extended()` with exactly the above two flags that
> we wanted to set in the first place.
> 
> Of course, this is pure luck, and this can break any moment. So let's
> fix this and correct the code to not pass any flags at all.