pkg/index: fix corpus AppendClaims use of signerFilter

Follow-up of ec66bcc871

This change should be the last of its kind, in the corpus at least, and
should make most searches and the web UI usable again, with both kinds
of hashes (sha1 and sha224).

Updates #537

Change-Id: Icfe9e8aaab031313612c555b7601895aeba16a7c

pkg/index/corpus.go

@@ -1297,13 +1297,28 @@ func (c *Corpus) AppendClaims(ctx context.Context, dst []camtypes.Claim, permaNo
 	if !ok {
 		return nil, nil
 	}
+
+	var signerRefs signerRefSet
+	if signerFilter.Valid() {
+		signer, ok := c.keyId[signerFilter]
+		if !ok {
+			return dst, nil
+		}
+		signerRefs, ok = c.signerRefs[signer]
+		if !ok {
+			return dst, nil
+		}
+	}
+
 	for _, cl := range pm.Claims {
 		if c.IsDeleted(cl.BlobRef) {
 			continue
 		}
-		if signerFilter.Valid() && cl.Signer != signerFilter {
+
+		if len(signerRefs) > 0 && !signerRefs.blobMatches(cl.Signer) {
 			continue
 		}
+
 		if attrFilter != "" && cl.Attr != attrFilter {
 			continue
 		}