js: properly reject pgp message without signature
js: properly reject pgp message without signature

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* A verify at gpgme-json does not fail if there is a valid pgp message
  that does not include a signature. Instead, the answer will be devoid
  of signatures. In javascript, the SIG_NO_SIG error should be reported
  here, but wasn't.

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme