Fix issue with not working select the last tab preference

[romamatusevich]

Test Plan:

1. Open https://github.com (tab 1)
2. Open about:preferences#tabs in a new tab (tab 2)
3. Set "Select the last viewed tab"
4. Open https://github.com/features in a new tab (tab 3)
5. Select tab 1
6. Select tab 3
7. Close tab 3

Expected result: tab 1 should be selected

Description

Pinned locations for frames were nullified and due to that check by last accessed time didn't work. Added null case and tests for getFrameByLastAccessedTime function.

Fix #8357

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

[Jacalz]

It is getting annoying with pinned tabs not working with this setting, would guess that it is not what this is fixing but it is related kinda 😉 #7332

[bsclifton]

Confirmed before/after- great work on this 😄

Love the tests! 👍