Added safe wrapper for toLocateDate() to handle null/invalid dates an…

[bsclifton]

• 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).

@bbondy: ** Would be great if this could make it into 0.12.9, but can be pushed to 0.12.10. I'll tentatively mark it as 0.12.9 and let you choose while merging** 😄

…d updated code on Bookmark Manager.

Fixes #5576

Auditors: @bbondy

Test Plan:

1. Launch Brave and open Bookmarks Manager
2. Click the import button and import a file as html
3. View the bookmarks in bookmarks manager. Notice the date is now empty (and not the epoch)

[bsclifton]

Here's what the bug looks like:

And here's what the fix looks like:

[bsclifton]

Moving to 0.12.10

[bbondy]

++