Filtering tags in statistics page - 404 page

[Elthan]

Tags in the statistics page include the page number query in the URL. This means that when filtering from, ex, the second page on a tag that does not have 2 pages worth of assignment it will lead to a 404 as the page does not exist.

Solved by either deleting page from URL in tags or redirecting automatically when does not find the page.

[torgeirl]

Steps to reproduce

• navigate to the second page of a course's statistics overview (example.com/a/1/statistics/?page=2)
• select a tag*

(Edit: * for some reason, semester tags aren't affected by this issue.)

I'm able to reproduce this with v3.0.0b13 (issue #102).

[torgeirl]

From our monitoring I noticed a similar URI that yields a HTTP 500: /?tags=&page=2. I have no idea how our users even ended up on there, but it might be useful for debugging.