message: Ignore img tags in HTML if src is not specified
  This applies to HTML messages and group summaries.
diff: @@ -208,7 +208,7 @@ const sanitizeHtmlParams = {
  // Strip out imgs that aren't `mxc` here instead of using allowedSchemesByTag
  // because transformTags is used _before_ we filter by allowedSchemesByTag and
  // we don't want to allow images with `https?` `src`s.
  - if (!attribs.src.startsWith('mxc://')) {
  + if (!attribs.src || !attribs.src.startsWith('mxc://')) {
  return { tagName, attribs: {}};
  }
  attribs.src = MatrixClientPeg.get().mxcUrlToHttp(
  