Floss: Propagate error at Option<T> decoding

When decoding Option<T>, it should propagate error if decoding T fails
instead of silently converting it to None.

Bug: 217274432
Tag: #floss
Test: Manual - intentionally call StartScan with improper ScanFilter

Change-Id: Ifeb66fc008df701ac0c56443c54c14dfcff8f319