Fatal errror when not uploading background image again after getting required-field reminder

[Rillke]

Sorry if this is a general bug of ILIAS and has been fixed in a newer version. I just currently have no current version of ILIAS available for testing.

When creating a paint question and forgetting to fill-in a required value and selecting an image background, an error will be thrown if the image is not selected again after filling the required fields. The fatal error will be always thrown when attempting to open the question.

Steps to reproduce:

1. Create a question pool and click "Create Question"
2. Select "Paint Question" as the type and use the richt-text editor
3. Fill all required fields except the points (0) AND select a background image
4. Press "save"
5. You'll get the following screen:
   
6. Note the " Value too low. Please enter a higher value." for points and "Pending file: ilias_silly_paint_question_export.PNG"
7. Enter 1 for points and press "save" again.
8. Click on "back to question pool"
9. Click the question you just created.
10. See fatal error.
    

[b1e3b] [2022-02-25 16:46:00.799689] unihalle_root.ERROR: ilErrorHandling::{closure}:50 2 getimagesize(/var/www/ilias/data/unihalle/assessment/332074/1321733/images/ilias_silly_paint_question_export.PNG): failed to open stream: No such file or directory in /var/www/ilias/Customizing/global/plugins/Modules/TestQuestionPool/Questions/assPaintQuestion/classes/class.assPaintQuestionGUI.php:287