openpgp: Change accessors to return all issuers.

  - Unlike the `Signature Creation Time` subpacket, there are
    legitimate reasons to have multiple `Issuer` subpackets and
    `Issuer Fingerprint` subpackets.

  - Rename `SubpacketAreas::issuer` to `SubpacketAreas::issuers` and
    return all `Issuer` subpackets.

  - Likewise, Rename `SubpacketAreas::issuer_fingerprint` to
    `SubpacketAreas::issuer_fingerprints` and return all `Issuer
    Fingerprint` subpackets.

  - Change `sq` to list all issuers.  Deduplicate first, however.

1 files changed, 3 insertions, 1 deletions

diff --git a/openpgp/src/packet/signature/mod.rs b/openpgp/src/packet/signature/mod.rs
index 407384a0..25f0a4fd 100644
--- a/openpgp/src/packet/signature/mod.rs
+++ b/openpgp/src/packet/signature/mod.rs
@@ -1380,7 +1380,9 @@ impl SignatureBuilder {
         }
 
         // Make sure we have an issuer packet.
-        if self.issuer().is_none() && self.issuer_fingerprint().is_none() {
+        if self.issuers().next().is_none()
+            && self.issuer_fingerprints().next().is_none()
+        {
             self = self.set_issuer(signer.public().keyid())?
                 .set_issuer_fingerprint(signer.public().fingerprint())?;
         }