Avoid slurping objects recursively in activity parsing

lib/activity.php

@@ -176,6 +176,10 @@ class Activity
         if ($objectEls->length > 0) {
             for ($i = 0; $i < $objectEls->length; $i++) {
                 $objectEl = $objectEls->item($i);
+                // Only immediate children (don't slurp embedded activities' objects!)
+                if ($objectEl->parentNode != $entry) {
+                    continue;
+                }
                 // Special case for embedded activities
                 $objectType = ActivityUtils::childContent($objectEl, self::OBJECTTYPE, self::SPEC);
                 if (!empty($objectType) && $objectType == ActivityObject::ACTIVITY) {