Aborted output extensions create an empty file

[jazzynico]

When an output extension fails, an unnecessary empty file is created.

Steps to reproduce:
1. Open a blank new document.
2. Use File>Save As, Gimp XCF output.
3. Accept the extension's parameters.
4. Since there's nothing to export, the extension fails and returns an error message.
5. An empty file is created in the location set in 2.

Also reproduced with SK1 export (when saving an empty document) and Compressed SVG+media (when debugging it...).

[jazzynico (jazzynico)]

Fix committed in the trunk, revision 9815.
Tested on Ubuntu 10.04, no apparent regression.

An additional message is sent by the extension system (not the python script!) to notify users that the file was not saved. This is a standard message which usually show when the file can't be written to the disk, but I feel it can be used here too. Tell me if you think it's not useful at all.

Please test!

[Alex Valavanis (valavanisalex)]

Attaching upstream patch for backport testing in Ubuntu.