0.18.20: Cannot create a new private/session tab without an active window

[cndouglas]

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

• Describe the issue you encountered:
  If there is no active window, you cannot create a private or session tab. The bug started occurring in Brave 0.18.20. Could it be due to Stop beach balling with this one simple trick #10305?

• Platform (Win7, 8, 10? macOS? Linux distro?):
  macOS 10.12.x

• Brave Version (revision SHA):
  0.18.20 (60bb9e6)

• Steps to reproduce:

  1. Open Brave.
  2. Close the window without quitting the app.
  3. Select Menubar > New Private Tab or press Shift+Cmd/Ctrl+P.

• Actual result:
  A new window with a normal tab is created.

• Expected result:
  A new window with a private tab is created.

• 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?
  No.

• Can this issue be consistently reproduced?
  Yes.

[cndouglas]

Likely related: #10376

[bbondy]

Duplicate of #10376