Q_Response::setMeta(): clear stale og:image companion tags when a later image can't be sized

[zattak1]

A page that sets og:image twice can end up advertising companion tags that describe the image that lost.

Cause

setMeta() derives four companions whenever an og:image is set and getimagesize() succeeds:

if (is_array($size) && !empty($size[0]) && !empty($size[1])) {
    self::setMeta(array(
        array(... "og:image:width",      $size[0]),
        array(... "og:image:height",     $size[1]),
        array(... "og:image:secure_url", $params["content"]),
        array(... "og:image:type",       $size["mime"])
    ));
}

og:image itself is stored as self::$metas[$key] keyed by name:value, so a second call replaces the first. The four companions are only ever written, never cleared — and only written when the size lookup succeeds.

So when a page sets a sizeable og:image first (an app default on local disk) and an unsizeable one second (a stream icon that is missing, or a remote URL), the survivors are the first image's:

<meta property="og:image:width"      content="400">
<meta property="og:image:height"     content="400">
<meta property="og:image:secure_url" content="https://example.com/img/icon/400.png">
<meta property="og:image:type"       content="image/png">
<meta property="og:image"            content="https://example.com/.../icon/1787355937/1000x.jpg">

og:image:secure_url names a different image from og:image, and the declared 400×400 / image/png describes neither. Unfurlers that prefer secure_url show the wrong image entirely; the rest advertise wrong dimensions.

Fix

og:image is well-formed on its own, so clear the stale set rather than leave it describing another image. Adds Q_Response::clearMeta(), which removes metas by key from both the global set and every slot.

Verified against a live install: with a correctly sized image the companions are rewritten as before (1000/1000/image/jpeg, secure_url == og:image); with an unsizeable one they are now absent rather than stale.