Possible fix for T668

Summary:
Always save the script, regardless of whether or not the object script
is empty, this way and default to the original script, unless the object
script has been changed. This way, the original interpreter should be
saved, unless the object script is changed

Test Plan:

1. open a report with a python interpreter
2. edit the report with an innocuous change (alter section height)
3. save report, confirm on debug output that the interpreter is still python
4. edit the report and change the script source
5. save, confirm the interpreter is now javascript

Reviewers: staniek

Reviewed By: staniek

Tags: KReport

Maniphest Tasks: T668

Differential Revision: https://phabricator.kde.org/D5700