Listing an empty certificate store should not be an error.

- `sq cert list` on an empty certificate store should not be an
    error.

src/common/pki/authenticate.rs

@@ -419,6 +419,10 @@ pub fn authenticate<'store, 'rstore>(
                 .sq().arg("network").arg("search")
                 .arg("some-mail-address")
                 .done();
+
+            // We're listing everything and we have nothing.  That's
+            // not actually an error.
+            return Ok(());
         }
     } else if bindings.len() - bindings_shown > 0 {
         // Some of the matching bindings were not shown.  Tell the

tests/integration/sq_cert_list.rs

@@ -39,3 +39,28 @@ fn list() {
     // When we use --email, then we don't do substring matching.
     assert!(sq.cert_list_maybe(&["--email", &email[1..]]).is_err());
 }
+
+#[test]
+fn list_empty() {
+    let sq = Sq::new();
+
+    // Listing an empty certificate store should not be an error.
+    sq.cert_list(&[]);
+
+    // Listing an empty certificate store with a pattern (that doesn't
+    // match anything) should be.
+    assert!(sq.cert_list_maybe(&["not found"]).is_err());
+
+    let (cert, cert_path, _rev_path)
+        = sq.key_generate(&[], &[ "alice" ]);
+    sq.key_import(cert_path);
+
+    // Not linked => error.
+    assert!(sq.cert_list_maybe(&["alice"]).is_err());
+    // Not found => error.
+    assert!(sq.cert_list_maybe(&["not found"]).is_err());
+
+    // Linked and found => ok.
+    sq.pki_link_add(&[], cert.key_handle(), &["alice"]);
+    sq.cert_list(&["alice"]);
+}