404 - Manage non-existent Fieldset

[skrolikowski]

Describe the issue

If a Fieldset isn't associated with a Matrix, the Link to edit that Fieldset leads to a 404 error.

To reproduce

• Create a Matrix (Page or Collection, doesn't matter; DO NOT assign a Fieldset).
• Click to add new Entry for Matrix.
• Click "Manage your page/collection" => 404 :(

Expected behavior

If no Fieldset is set for Matrix, then redirect to matrix edit page.

Screenshots

Bug report checklist

• I have filled out as much information as I can
• I have detailed how the issue can be reproduced
• I have searched for existing issues and to the best of my knowledge this is not a duplicate