Tweaked wfThumbIsStandard() to recognize handler-specific default parameters

* Now thumbnails with default lossy/lossless values will still count as "standard",
  for example. This makes use of the file media handler.

Change-Id: Ia69301dfbf85bb26a17f8eee0939d690021343ec
(cherry picked from commit b0de7c7c60eb2f8464d6b6eb653331bdf80e34b0)