Theoretical fix for some crashes

[zadjii-msft]

Found this while looking through dumps for failure f544cf8e-1879-c59b-3f0b-1a364b92b974. That's MSFT:45210947. (1% of our 1.19 crashes)

From the dump I looked at,

Looks like,

• we're on Windows 10
• We're refrigerating a window
• We are pumping the remaining XAML messages as we refrigerate (_pumpRemainingXamlMessages)
• In there, we're finally getting the TerminalPage::_CompleteInitialization
• that calls up to the _root->Initialized lambda set up in TerminalWindow::Initialize
• There it tries to get the launch mode from the settings, and explodes. Presumably _settings is null, but can't see in this dump.

so the window is closing before it's initialized.

When we _warmWindow = std::move(_host->Refrigerate()), we call AppHost::Refrigerate, which will null out the TerminalWindow. So when we're getting to TerminalWindow::Initialize, we're calling that on a nullptr. That's the trick.

We need to revoke the internal Initialized callback. Which makes sense. It's a lambda that binds this 🤦

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After more looking, it really doesn't seem like the stacks that are tracked in f544cf8e-1879-c59b-3f0b-1a364b92b974 look like the same stack that I was debugging, but this is a realy issue regardless.

[zadjii-msft]

note: I'm not sure I could repro this locally. This is more of a "well, look at the code, that's definitely a bug" fix.