Oops, "magic eight" is necessary here afterall

Oops, "magic eight" is necessary here afterall

- Fix regression from commit 807b402d95702f3f91e9e2bfbd2b5ca8c9964ed9,
  the array gets passed as a pointer (how else would it work at all),
  so despite having seemingly correct type, sizeof(keyid) depends
  on the pointer size. This happens to be 8 on x86_64 and friends
  but breaks pgp fingerprint calculation on eg i386.
- Also return the explicit size from pgpExtractPubkeyFingerprint(),
  this has been "broken" for much longer but then all callers should
  really care about is -1 for error.