Null check macOS window handle before detaching view

[gxalpha]

Description

Fixes a crash with service integrations. What the original code does is decoupling the browser from the widget (more explanation is in the comment a few lines above the modified). For some reason however, on Qt 6 the window handle can be null sometimes. In that case, trying to detach the view from the view from the superview fails (obviously).

By the way, the code looks cursed for two reasons: 1) It's Objective-C in a C(++) file 2) It was unreadable even before. If desired I can untangle the original code.

Motivation and Context

Don't want crashes.

How Has This Been Tested?

macOS 13. No more crashes with Twitch integration.

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.

[WizardCM]

Also we can save untangling the code for post-28 in my opinion.