Fix "add more metadata" fatal in Pholio

Summary: Ref T13332. This fix isn't terribly satisfying, but resolves the issue: this behavior may attempt to build HTML blocks with metadata after Javascript footer rendering has started. Use `hsprintf()` to flatten the markup earlier.

Test Plan: Put a `T123` reference in the description of a Pholio image, then loaded a mock.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13332

Differential Revision: https://secure.phabricator.com/D20647

src/applications/pholio/view/PholioMockImagesView.php

@@ -103,7 +103,7 @@ final class PholioMockImagesView extends AphrontView {
         'width' => $x,
         'height' => $y,
         'title' => $image->getName(),
-        'descriptionMarkup' => $description,
+        'descriptionMarkup' => hsprintf('%s', $description),
         'isObsolete' => (bool)$image->getIsObsolete(),
         'isImage' => $file->isViewableImage(),
         'isViewable' => $file->isViewableInBrowser(),