Bugfix:
Sharepoint LibraryFolder scopes always return
zero matches in filtering with a prefix due to the
path not having the drive root prefix truncated, as is
expected of onedrive-based storage paths.
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#### Does this PR need a docs update or release note?
- [x] ✅ Yes, it's included
#### Type of change
- [x] 🐛 Bugfix
#### Test Plan
- [x] 💪 Manual
- [x] ⚡ Unit test