REALLY don't allow browser docks to arbitrarily close OBS

[WizardCM]

Description

• See #427

Motivation and Context

The previous solution only worked for code that ran after the page had finished loading. I was hoping that'd solve the problem for most users, which it didn't. But even if it did, we still don't want browser docks to be able to arbitrarily close the main OBS window.

• See #427

How Has This Been Tested?

Implement a page that calls window.close() immediately.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.

[RytoEX]

Is there a test page I can use to test this, or do I need to create one myself?