sortHeader() concatenated $_REQUEST['filter']['query'] into the href of
every export view column header without escaping, allowing reflected
HTML injection (iframe, meta refresh, style) via a crafted link. Pass it
through validHtmlStr() like the other request values in the same string
are passed through validInt()/validCardinal().
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit 7517018879f2be9ba1f9439e3364686ccee226ed)