fix(ObjectStorePreviewStorage): Close count stream wrapper - #63849

/backport to stable35

/backport to stable34

/backport to stable33

Production data point in favour of backporting this to stable34.

We hit this on 34.0.2 with OpenStack Swift as primary storage. writePreview() returns $size = 0 on every call because Swift::writeObject() never closes the stream it is handed, so the CountWrapper callback never fires. savePreview() then throws Unable to write preview file even though the upload to Swift succeeded.

The impact is bigger than log noise, because the preview is never recorded in oc_previews:

• No preview has been cached since the 34 upgrade. Last row in oc_previews is 2026-08-10 00:38, hours before we upgraded that morning — 21 days, zero new rows, against 14,781 image files.
• Every thumbnail request regenerates from scratch, indefinitely. ~99% of the failures are GET /core/preview, and a 32×32 request still goes through getMaxPreview(), so each one fully decodes the source and builds a 4096×4096 preview.
• Orphaned objects accumulate. The upload succeeds before the throw, so each attempt leaves an object nothing will ever read: 26,306 objects / 10.5 GB in 21 days, ~34% of all objects in the container.
• On a small (4 GB) instance this exhausted memory and required a hard reset.

For comparison the files path gets this right — ObjectStoreStorage::writeStream() closes the count stream before reading the size:

$this->objectStore->writeObject($urn, $countStream, ...);
if (is_resource($countStream)) {
    fclose($countStream);
}
$stat['size'] = $totalWritten;

Carrying this patch locally meanwhile; it applies cleanly to 34.0.2. Happy to test a stable34 backport.