Improve the error message when you enter a negative grade when using a marking guide

Visit (or create) a course that has a least 1 student enrolled. Create an assignment with the 'Grading method' set to 'Marking guide'. Click on the assignment then on 'Advanced grading' under 'Assignment administration'. Click on 'Define new grading for from scatch' Under 'Maximum mark' enter a negative value and submit the form. Ensure you get the warning 'The max score is not valid, negative values are not allowed'. Fill out the form correctly and submit. Click on the assignment then on 'View/grade all submissions'. Click on the 'grade' icon next to a student. Enter a negative grade. Ensure you get the warning 'The score given to '<Criterion name>' is not valid, negative values are not allowed'. Fill out the form correctly and ensure you can submit successfully.