message: fix: allow omemo messages without authentication tag
  doesn't require authentication tags and therefore we don't
  require them either.
diff: @@ -16,6 +16,7 @@ import { Strophe } from '../../../vendor/Strophe'
  import BundleManager from './BundleManager';
  import IdentityManager from './IdentityManager';
  import Translation from '@util/Translation';
  +import Log from '@util/Log';
  export default class Omemo {
  private store: Store;
  @@ -179,9 +180,13 @@ export default class Omemo {
  let authenticationTag = exportedKey.slice(16);
  if (authenticationTag.byteLength < 16) {
  + if (authenticationTag.byteLength > 0) {
  throw new Error('Authentication tag too short');
  }
  + Log.info(`Authentication tag is only ${authenticationTag.byteLength} byte long`);
  + }
  +
  if (!encryptedData.payload) {
  throw new Error('We received a KeyTransportElement');
  }
  