#4 setting's option "usedefaultoutputfile" works improperly

[Dmitry Valento]

Every time, when a project's properties are applied and saved, radiobutton "Do you want to be asked ..." changes its state to opposite.

Steps to reproduce:

1. Open a project's properties
2. Select tab "Video export". Just notice (do not change!) the position of radiobutton "Do you want to be asked ..."
3. Press "Apply"
4. Press "File|Save"
5. Open a project's properties
6. Select tab "Video export".
7. Bug: the position of radiobutton "Do you want to be asked ..." has been changed!

[Dmitry Valento]

This bug has been fixed in branch ticket4_fix_property_usedefaultoutputfile