exportExerciseAllResultsZip don't give the results of the exercise in v2

[Coussecousse]

Describe
After refactoring export_exercise_results.php, I noticed that the downloaded PDF is blank except for the header.

To Reproduce
Steps to reproduce the behavior:

1. Go to /main/admin/export_exercise_results.php once it's merged
2. Fill in the different fields
3. Click Export
4. Check the generated PDF.

Expected behavior
The PDF should display the results of the different exercises — similar to how it worked in the old version of Chamilo.(?)

Screenshots

Desktop (please complete the following information):

• OS: Linux Ubuntu 22.04
• Browser: Chrome

**Server

• OS: Linux Ubuntu 22.04
• Version of Chamilo: v2
• Version of PHP: 8.3

Additionnel informations :
Check exportExerciseAllResultsZip in exercice.lib.php