Don't use Optional in fingerprints_by_id
Don't use Optional in fingerprints_by_id

This does not really speed up the program, but it does save a little
bit of memory in a very performance critical code path, with very little
extra bloat in the code.

per-gron/shuriken,per-gron/shuriken,per-gron/shuriken,per-gron/shuriken