Investigate orphaned records

Keys with the (undocumented) key prefix: 00 00 00 00 32 appear to contain deleted data records sometimes.

Need to look at how the records can be recovered (when they are records, because they aren't always).

Related to scopes: https://github.com/chromium/chromium/tree/master/components/services/storage/indexed_db/scopes

See: ScopesEncoder::UndoTaskKeyPrefix

Some of this functionality is in the library's back-end now, but we're not currently doing anything with it as I'm still not sure about the best (and safest) way to exploit it.