Fix auto scroll to wait until discussion is loaded
Fix auto scroll to wait until discussion is loaded

fixes VICE-2435

Test Plan
1. Load a discussion in Legacy Discussions
2. Find a discussion ID (Hint: The ID is in the HTML)
3. Appnd #entry-NNNN (Your ID) to the URL and load
4. Expected: Page should auto scroll to entry when loaded
5. Now delete $entry-NNNN frmo the URL
6. Append /entry-NNNN and hit enter
7: Expected: Page should auto scroll to entry when loaded like Step 4

Change-Id: I74c661743a9b6cc1ada7292087282cd7293f1193
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/285760
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Jason Gillett <12d37bea14b8257b31fd2f970455158adbd46adb@instructure.com>
Product-Review: Jason Gillett <12d37bea14b8257b31fd2f970455158adbd46adb@instructure.com>
QA-Review: Chawn Neal <908eabd8c84ff6c7c139535b8d37802d58ad1683@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms