message: Say when backup is signed by unknown device
  rather than say it isn't signed by any devices
  Requires
diff: @@ -186,18 +186,23 @@ export default class KeyBackupPanel extends React.PureComponent {
  }
  let backupSigStatuses = this.state.backupSigStatus.sigs.map((sig, i) => {
  - const deviceName = sig.device.getDisplayName() || sig.device.deviceId;
  + const deviceName = sig.device ? (sig.device.getDisplayName() || sig.device.deviceId) : null;
  const validity = sub =>
  <span className={sig.valid ? 'mx_KeyBackupPanel_sigValid' : 'mx_KeyBackupPanel_sigInvalid'}>
  {sub}
  </span>;
  const verify = sub =>
  - <span className={sig.device.isVerified() ? 'mx_KeyBackupPanel_deviceVerified' : 'mx_KeyBackupPanel_deviceNotVerified'}>
  + <span className={sig.device && sig.device.isVerified() ? 'mx_KeyBackupPanel_deviceVerified' : 'mx_KeyBackupPanel_deviceNotVerified'}>
  {sub}
  </span>;
  const device = sub => <span className="mx_KeyBackupPanel_deviceName">{deviceName}</span>;
  let sigStatus;
  - if (sig.device.getFingerprint() === MatrixClientPeg.get().getDeviceEd25519Key()) {
  + if (!sig.device) {
  + sigStatus = _t(
  + "Backup has a signature from <verify>unknown</verify> device with ID %(deviceId)s.",
  + { deviceId: sig.deviceId }, { verify },
  + );
  + } else if (sig.device.getFingerprint() === MatrixClientPeg.get().getDeviceEd25519Key()) {
  sigStatus = _t(
  "Backup has a <validity>valid</validity> signature from this device",
  {}, { validity },
  @@ -229,7 +234,7 @@ export default class KeyBackupPanel extends React.PureComponent {
  }
  let verifyButton;
  - if (!sig.device.isVerified()) {
  + if (!sig.device || !sig.device.isVerified()) {
  verifyButton = <div><br /><AccessibleButton className="mx_UserSettings_button"
  onClick={this._verifyDevice} data-sigindex={i}>
  { _t("Verify...") }
  