fix(bs): correctly passing additional I/O flags to blob store

[dsavitskiy]

No description provided.

[dsavitskiy]

A flag that is used to determine unallocated blocks for rebuild of thin-provisioned volumes, was passed to Blobstore internals incorrectly. This only happened for recursive code path, which works for snapshots only. It didn’t happen for thin provisioned vol code path, as it does not go recursively into underlying blobstore (it terminates in special zero-filled blob store instead).

Because of that, an invalid value could sometimes be read from that flag, resulting in read I/O failure with false DeallocatedOrUnwrittenBlock error. Potentially, as a pointer to an incompatible struct was dereferenced, it could crash.