Draft: print: Reject enroll images that can't be matched

If the score of a print matching itself is too low to match, then reject it. It can never match and it is therefore completely useless.

Also change this into a non-fatal error, the user is free to retry the enroll step in the hope that more minutiae is found (e.g. longer swipe).

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I have no idea right now whether this works, but it seems like a reasonable thing to do.