Don't explode when we tear out the last tab of the window (#15259)

If you were really fast, and closed one window, and then tried to drag
the only tab out of the last remaining window, the Terminal could
explode. It'd attempt to restore the previous window state, and explode.

Easy way to stop this (also, be more robust): just don't attempt to
restore windows during tear-out. That's obvious.

This is a part of #14957

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -168,8 +168,8 @@ void AppHost::_HandleCommandlineArgs(const Remoting::WindowRequestedArgs& window
     if (_peasant)
     {
         const auto& args{ _peasant.InitialArgs() };
-
-        if (!windowArgs.Content().empty())
+        const bool startedForContent = !windowArgs.Content().empty();
+        if (startedForContent)
         {
             _windowLogic.SetStartupContent(windowArgs.Content(), windowArgs.InitialBounds());
         }
@@ -220,7 +220,8 @@ void AppHost::_HandleCommandlineArgs(const Remoting::WindowRequestedArgs& window
         // seemed to reorder bits of init so much that everything broke. So
         // we'll leave it here.
         const auto numPeasants = _windowManager.GetNumberOfPeasants();
-        if (numPeasants == 1)
+        // Don't attempt to session restore if we're just making a window for tear-out
+        if (!startedForContent && numPeasants == 1)
         {
             const auto layouts = ApplicationState::SharedInstance().PersistedWindowLayouts();
             if (_appLogic.ShouldUsePersistedLayout() &&