FIX: image resizer service not handling certain filenames.

Hi,
To test this one, try adding an image with file name examplejpg.jpg .
Derivative image datastreams were not being created for this edge-case.
Then apply this and try again to test.

The edge case is a name like "examplejpg.jpg".
The system was failing to put the $ext extension on.
Derivative images like web_ , thumbnail_ and preview_ were not being generated.