format: Viewable Images Bug

This addresses a small bug where `Format::viewableImages()` was using
unencoded quotes instead of encoded quotes to replace the `<img src=`
matches. This means when the content is added to a textarea’s
`draft-data-original` attribute the unencoded quotes break the attribute
and displays raw HTML content. This moves the `Format::htmlchars()` call
after the `preg_replace_callback()` so the quotes can be properly
encoded (if needed).

include/class.format.php

@@ -588,16 +588,15 @@ static function viewableImages($html, $options=array(), $format=false) {
         $cids = $images = array();
         $options +=array(
                 'disposition' => 'inline');
-        if ($format)
-            $html = Format::htmlchars($html, true);
-        return preg_replace_callback('/("|")cid:([\w._-]{32})("|")/',
+        $html = preg_replace_callback('/("|")cid:([\w._-]{32})("|")/',
         function($match) use ($options, $images) {
             if (!($file = AttachmentFile::lookup($match[2])))
                 return $match[0];
 
             return sprintf('"%s" data-cid="%s"',
                 $file->getDownloadUrl($options), $match[2]);
         }, $html);
+        return $format ? Format::htmlchars($html, true) : $html;
     }