Merge pull request #3867 from matrix-org/travis/fix-messagepanel-ref

Fix error about MessagePanel not being available for read markers

Author: jryans

src/components/structures/TimelinePanel.js

@@ -1136,7 +1136,9 @@ const TimelinePanel = createReactClass({
  const messagePanel = this._messagePanel.current;
  if (messagePanel === undefined) return null;
 
- const wrapperRect = ReactDOM.findDOMNode(messagePanel).getBoundingClientRect();
+ const messagePanelNode = ReactDOM.findDOMNode(messagePanel);
+ if (!messagePanelNode) return null; // sometimes this happens for fresh rooms/post-sync
+ const wrapperRect = messagePanelNode.getBoundingClientRect();
  const myUserId = MatrixClientPeg.get().credentials.userId;
 
  const isNodeInView = (node) => {