Fix [10-Oct-2014 15:08:03] PHP Fatal error:  Cannot access protected property MediaTransformError::$height in ..\extensions\ImageTagging\ImageTagging_body.php on line 315

This would happen when the Special:TaggedImages page would contain one or
more "images" where the actual image file was, for one reason or another,
missing. Now missing images no longer break the special page.

Change-Id: I5709fd4fc90adbdfa9b0dc2bb5fe0dafa68dc80d