Workshop/Submissions - Form doesn't check title field for only whitespace

When creating a new submission, the user is able to enter titles consisting only of whitespace.

Doing so, a user is not able to click any link to this particular submission in the later "Assessment phase". Links to the submission are rendered as empty a-tags (<a href="..."></a>) making assessment impossible.

This behaviour can be reproduced on https://sandbox.moodledemo.net/

Steps to reproduce

1. Login as teacher
2. Create a workshop, configure it and move to the "Submission phase"

1. Login as student1
2. Access the workshop
3. Create a submission with a title consisting only of whitespace (eg. one space character)

1. Login as teacher
2. Access the workshop
3. Allocate Submissions (student2 reviews student1)
4. Move to the "Assessment phase"

1. Login as student2
2. Access the workshop
3. Try to grade the submission from student 1

Expected Result

Student2 is able to click the submission.

Actual Result

Student2 is not able to click the submission. The link is not visible.