message: Fix copy button on code blocks when there is no code just pre
diff: @@ -278,7 +278,7 @@ export default createReactClass({
  const button = document.createElement("span");
  button.className = "mx_EventTile_copyButton";
  button.onclick = (e) => {
  - const copyCode = button.parentNode.getElementsByTagName("code")[0];
  + const copyCode = button.parentNode.getElementsByTagName("pre")[0];
  const successful = this.copyToClipboard(copyCode.textContent);
  const buttonRect = e.target.getBoundingClientRect();
  