message: make command detection more resilient
diff: @@ -170,7 +170,19 @@ export default class SendMessageComposer extends React.Component {
  _isSlashCommand() {
  const parts = this.model.parts;
  - return parts.length && parts[0].type === "command";
  + const firstPart = parts[0];
  + if (firstPart) {
  + if (firstPart.type === "command") {
  + return true;
  + }
  + // be extra resilient when somehow the AutocompleteWrapperModel or
  + // CommandPartCreator fails to insert a command part, so we don't send
  + // a command as a message
  + if (firstPart.type === "plain" && firstPart.text.startsWith("/")) {
  + return true;
  + }
  + }
  + return false;
  }
  async _runSlashCommand() {
  