Fix "N changed files" link toggler jumping to top

What does this MR do?

Fix clicking on "N changed files" link toggler jumping scroll to the top.

Thanks for spotting @DouweM, https://gitlab.slack.com/archives/C0GQHHPGW/p1490132124022958

Are there points in the code the reviewer needs to double check?

• See previous MR; https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9943
• See subsequent MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9918

Togglers to check:

• "Create a Mattermost team for this group" Checkbox, http://localhost:3000/groups/new (enable mattermost in config/gitlab.yml)
• "Repo by Url" button, http://localhost:3000/projects/new
• In MR widget "Modify commit message", http://localhost:3000/gitlab-org/gitlab-ce/merge_requests/9
• Discussion "Toggle discussion", http://localhost:3000/gitlab-org/gitlab-ce/merge_requests/3
• "Showing 1 changed file with 4 additions and 7 deletions" , http://localhost:3000/gitlab-org/gitlab-ce/merge_requests/3/diffs
• Commit description toggle "...", http://localhost:3000/gitlab-org/gitlab-ce/commits/master

Why was this MR needed?

Clicking "N changed files" on MR diff view was jumping the scroll to the top with empty # fragment hash in the URL.

Does this MR meet the acceptance criteria?

• Tests
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #29414 (closed)

Nice job @MadLittleMods

marked the task All builds are passing as completed

@alfredo1 Friendly ping for review

approved this merge request

changed milestone to %9.1

removed ~149423 label

Thanks @MadLittleMods LGTM!

I'm changing this to 9.1 since 9.0 was released today.

merged

mentioned in commit 011664fd

changed milestone to %9.0

added ~149423 label

Reference to why we put it back on 9.0, https://gitlab.slack.com/archives/C0GQHHPGW/p1490386522721900

mentioned in issue #29872 (closed)

mentioned in commit 0ff30468

Picked into 9-0-stable and will go out in 9.0.1

removed ~149423 label