PEC thumbnails don't have a file extension

[MichaelRBond]

The combined thumbnail for PEC derivatives don't have a file extension. I've updated the export script to find the items without extensions as well as those with extensions. But, this needs updated.

[MichaelRBond]

Once this has been corrected, the items with missed extensions should be set to be reprocessed. (This can be scripted instead of doing it by hand.)