Accessibility: Fixed small issue with managing focus in the help dialog

Fixes CNVS-10696

Test plan:
- In sure that the help action is installed and working.
- Click the help button from the bottom of any page.
- Click the option to report a problem.
- Confirm that focus is set to the first form field and a user can start
  typing immediately.
- log in as a student and repeat the previous steps, except click the link to
  provide feedback for the instructur from within the help dialog.

Change-Id: Ic0e6e2bf8e5d73cb69cce661051856dc0b901867
Reviewed-on: https://gerrit.instructure.com/29092
Reviewed-by: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
Tested-by: Bryan Madsen <bryan@instructure.com>