Make sure we dont access an invalid optional on close (#11857)

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## Summary of the Pull Request
Clean up an invalid access that I introduced in #11440

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## References

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## PR Checklist
* [x] Closes #11684
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Documentation updated. If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/terminal) and link it here: #xxx
* [ ] Schema updated.
* [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

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## Detailed Description of the Pull Request / Additional comments

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## Validation Steps Performed

(cherry picked from commit 29e6235)

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -402,9 +402,14 @@ void AppHost::LastTabClosed(const winrt::Windows::Foundation::IInspectable& /*se
         _HideNotificationIconRequested();
     }
 
-    // We don't want to try to save layouts if we are about to close
+    // We don't want to try to save layouts if we are about to close.
     _getWindowLayoutThrottler.reset();
     _windowManager.GetWindowLayoutRequested(_GetWindowLayoutRequestedToken);
+    // We also don't need to update any of our bookkeeping on how many
+    // windows are open.
+    _windowManager.WindowCreated(_WindowCreatedToken);
+    _windowManager.WindowClosed(_WindowClosedToken);
+
     // Remove ourself from the list of peasants so that we aren't included in
     // any future requests. This will also mean we block until any existing
     // event handler finishes.
@@ -812,11 +817,17 @@ void AppHost::_BecomeMonarch(const winrt::Windows::Foundation::IInspectable& /*s
     // and subscribe for updates if there are any changes to that number.
     _logic.SetNumberOfOpenWindows(_windowManager.GetNumberOfPeasants());
 
-    _windowManager.WindowCreated([this](auto&&, auto&&) {
-        _getWindowLayoutThrottler.value()();
+    _WindowCreatedToken = _windowManager.WindowCreated([this](auto&&, auto&&) {
+        if (_getWindowLayoutThrottler) {
+            _getWindowLayoutThrottler.value()();
+        }
         _logic.SetNumberOfOpenWindows(_windowManager.GetNumberOfPeasants()); });
-    _windowManager.WindowClosed([this](auto&&, auto&&) {
-        _getWindowLayoutThrottler.value()();
+
+    _WindowClosedToken = _windowManager.WindowClosed([this](auto&&, auto&&) {
+        if (_getWindowLayoutThrottler)
+        {
+            _getWindowLayoutThrottler.value()();
+        }
         _logic.SetNumberOfOpenWindows(_windowManager.GetNumberOfPeasants());
     });
 

src/cascadia/WindowsTerminal/AppHost.h

@@ -115,4 +115,6 @@ class AppHost
     winrt::event_token _ShowNotificationIconContextMenuToken;
     winrt::event_token _NotificationIconMenuItemSelectedToken;
     winrt::event_token _GetWindowLayoutRequestedToken;
+    winrt::event_token _WindowCreatedToken;
+    winrt::event_token _WindowClosedToken;
 };