Switching between pages should reset comparison mode

[timkung]

It looks like when you enter the comparison mode when viewing history of a Page, it keeps the state of which versions are being compared as well as the comparison mode being toggled on.

This can cause an issue where you compare versions of a Page, and then switch to view the history of another Page which doesn't have the same versions as the previous Page and this causes a 404 (and broken UI), as it automatically calls the following URL as soon as you click on the History tab: /admin/historyviewer/schema/compareForm/<page-id>?RecordVersionFrom=<previous-from-version-id>&RecordVersionTo=<previous-to-version-id>&RecordClass=Page&RecordID=<page-id>

Steps to reproduce:

1. Create 2 new Pages
2. Create 4 versions on one of those Pages
3. Go to the History tab for the Page with 4 versions
4. Toggle the comparison mode and select version 4 and 3
5. Go to the second page
6. Click the History tab
7. See 404 error

Found using version 1.3.0.