message: If unspecified, don't crash if missing thumbnail info
  applies to stickers/images.
  We might want to consider to do that is better than assuming a aspect
  ratio of 600 x 800 (4:3).
diff: @@ -185,7 +185,7 @@ export default class extends React.Component {
  const content = this.props.mxEvent.getContent();
  if (content.file !== undefined && this.state.decryptedUrl === null) {
  let thumbnailPromise = Promise.resolve(null);
  - if (content.info.thumbnail_file) {
  + if (content.info && content.info.thumbnail_file) {
  thumbnailPromise = decryptFile(
  content.info.thumbnail_file,
  ).then(function(blob) {
  @@ -239,11 +239,20 @@ export default class extends React.Component {
  }
  _messageContent(contentUrl, thumbUrl, content) {
  + // If unspecifide in the thumbnail info, assume width x height to be 800 x 600.
  + let infoHeight = 600;
  + let infoWidth = 800;
  +
  + if (content.info && content.info.h && content.info.w) {
  + infoHeight = content.info.h;
  + infoWidth = content.info.w;
  + }
  +
  // The maximum height of the thumbnail as it is rendered as an <img>
  - const maxHeight = Math.min(this.props.maxImageHeight || 600, content.info.h);
  + const maxHeight = Math.min(this.props.maxImageHeight || 600, infoHeight);
  // The maximum width of the thumbnail, as dictated by its natural
  // maximum height.
  - const maxWidth = content.info.w * maxHeight / content.info.h;
  + const maxWidth = infoWidth * maxHeight / infoHeight;
  let img = null;
  let placeholder = null;
  @@ -274,12 +283,12 @@ export default class extends React.Component {
  const thumbnail = (
  <div className="mx_MImageBody_thumbnail_container" style={{ "max-height": maxHeight + "px" }} >
  { /* Calculate aspect ratio, using %padding will size _container correctly */ }
  - <div style={{ paddingBottom: (100 * content.info.h / content.info.w) + '%' }}></div>
  + <div style={{ paddingBottom: (100 * infoHeight / infoWidth) + '%' }}></div>
  { showPlaceholder &&
  <div className="mx_MImageBody_thumbnail" style={{
  // Constrain width here so that spinner appears central to the loaded thumbnail
  - "max-width": content.info.w + "px",
  + "max-width": infoWidth + "px",
  }}>
  <div className="mx_MImageBody_thumbnail_spinner">
  { placeholder }
  