Comment 14 for bug 650890

Fix committed in the trunk (revision 9802) and in the 0.48.x branch (revision 9678). I've also added a fix that removes the temporary folder when the extension has finished (successfully or not) its job.

I've reproduced the empty file error with the sk1 extension, and thus I guess it's not directly related to XCF and can be reported as a separate report.