message: avoid null-refs when receiving an action before initial rendering
diff: @@ -240,7 +240,7 @@ export default class SendMessageComposer extends React.Component {
  switch (payload.action) {
  case 'reply_to_event':
  case 'focus_composer':
  - this._editorRef.focus();
  + this._editorRef && this._editorRef.focus();
  break;
  case 'insert_mention':
  this._insertMention(payload.user_id);
  @@ -258,7 +258,7 @@ export default class SendMessageComposer extends React.Component {
  const userPillPart = this.model.partCreator.userPill(displayName, userId);
  this.model.insertPartsAt([userPillPart], this._editorRef.getCaret());
  // refocus on composer, as we just clicked "Mention"
  - this._editorRef.focus();
  + this._editorRef && this._editorRef.focus();
  }
  _insertQuotedMessage(event) {
  @@ -269,7 +269,7 @@ export default class SendMessageComposer extends React.Component {
  quoteParts.push(partCreator.newline());
  this.model.insertPartsAt(quoteParts, {offset: 0});
  // refocus on composer, as we just clicked "Quote"
  - this._editorRef.focus();
  + this._editorRef && this._editorRef.focus();
  }
  render() {
  