[OSCrypt] Decrypt data that was encrypted with empty key

If the data wasn't decrypted with the encryption key, OSCrypt tries
again, using an empty key.

This ensures data remains available, after restoring encryption keys.

Bug: 1195256
Change-Id: I609511350657a2d3ef930c584ceed282e227e93a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4318564


Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Christos Froussios <cfroussios@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1118445}