In Survey activity the Response report - The question does not work when debugging is active and not all answers are sent.

Description

Once the admin user creates a survey type COLLES (current) and it is answered by any user, the survey graphs are not displaying in the "Questions" item within the response reports.

Steps to replicate

1. Login as an admin.
2. Access to "Site administration > Development > Debugging" and make sure Debug level is set to developer.
3. Create a new course and enroll one student.
4. Add a "Survey" activity to a course; Survey type: "COLLES (Actual)".
5. Login as a student and add a random answer. Tick all radio buttons but leave 'How long did this survey take you to complete?' and 'Do you have any other comments?' empty
6. Submit your answer by pushing the button "Click here to continue".
7. Login as an admin.
8. From the activity cog, choose "Question" from the "Response report" section.

Observed   behavior

 The Survey graphs should be displayed

Expected behavior

 If you scroll there will be broken graph image