Students cannot delete uploaded files from the "Advanced uploading" assignment.

Steps to reproduce (Advanced uploading)
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• Create an "Advanced uploading" assignment with no due date, send for marking turned off, maximum number of files 1 and allow deleting
• As student, upload a file and submit
• As student, return to the assignment and click "Edit these files"
• Click the button next to the file and select 'Delete...'
• Click 'Save changes'

Expected result
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The uploaded file should be deleted.

Actual result
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An error message appears, "No file was found - are you sure you selected one to upload?"