message: Set max-width for thread summary on narrow message panel
diff: @@ -704,7 +704,7 @@ $threadInfoLineHeight: calc(2 * $font-12px); // See: _commons.scss
  .mx_MessagePanel_narrow .mx_ThreadSummary {
  min-width: initial;
  - max-width: initial;
  + max-width: 100%; // prevent overflow
  width: initial;
  }
  