message: Fix context when using subtree of components
diff: @@ -145,10 +145,12 @@ export default class MessageActionBar extends React.PureComponent {
  let editButton;
  if (isContentActionable(this.props.mxEvent)) {
  - if (this.context.room.canReact) {
  + // `context` can be null in tests that use a subtree of components
  + // that don't create the context.
  + if (!this.context || !this.context.room || this.context.room.canReact) {
  reactButton = this.renderReactButton();
  }
  - if (this.context.room.canReply) {
  + if (!this.context || !this.context.room || this.context.room.canReply) {
  replyButton = <span className="mx_MessageActionBar_maskButton mx_MessageActionBar_replyButton"
  title={_t("Reply")}
  onClick={this.onReplyClick}
  