white tab displayed if 'last viewed tab' isn't available

[LaurenWags]

• Did you search for similar issues before submitting this one?
  Yes

• Describe the issue you encountered:
  When the setting for 'When closing an active tab' is set to 'Select the last viewed tab', and you close the first tab (of two tabs), this results in a white tab being displayed.

• Platform (Win7, 8, 10? macOS? Linux distro?):
  MacOS

• Brave Version (revision SHA):
  Brave | 0.19.3
  rev | 053c863
  Muon | 4.4.9

• Steps to reproduce:

  1. Verify in Preferences > Tabs you have 'Select the last viewed tab' as the setting for 'When closing an active tab.
  2. Start with a new window (just one new tab).
  3. In the new tab navigate to a site like theverge.com.
  4. Cmd+click (MacOS) on a link to open a link in a new tab but not switch to it. (you now have two tabs).
  5. Cmd+w to close the active (first) tab.

• Actual result:
  White tab is displayed.

• Expected result:
  I was expecting to see the second tab since I closed the first one in the window.

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes

• Is this an issue in the currently released version?
  Yes (0.18.23)

• Can this issue be consistently reproduced?
  Yes

• Extra QA steps:

  1. Close the active tab in other ways (right click on tab > select Close tab, close active tab with X).

• Screenshot if needed:
  

• Any related issues:

[bsclifton]

I believe this will be fixed with @bbondy's upcoming changes