Allow creating new windows on another virtual desktop (#19458)

Whoops. Closes #18652

<DHowett> I chatted with Leonard to figure out why I kept
misunderstanding this PR. The key is that **this function should not
always return an existing window.** It's supposed to find an existing
window on the current virtual desktop, not literally any window
anywhere.

Author: lhecker

src/cascadia/WindowsTerminal/WindowEmperor.cpp

@@ -670,7 +670,8 @@ void WindowEmperor::_dispatchCommandlineCommon(winrt::array_view<const winrt::hs
 // This is an implementation-detail of _dispatchCommandline().
 safe_void_coroutine WindowEmperor::_dispatchCommandlineCurrentDesktop(winrt::TerminalApp::CommandlineArgs args)
 {
-    std::weak_ptr<AppHost> mostRecentWeak;
+    std::shared_ptr<AppHost> mostRecent;
+    AppHost* window = nullptr;
 
     if (winrt::guid currentDesktop; VirtualDesktopUtils::GetCurrentVirtualDesktopId(reinterpret_cast<GUID*>(&currentDesktop)))
     {
@@ -682,19 +683,18 @@ safe_void_coroutine WindowEmperor::_dispatchCommandlineCurrentDesktop(winrt::Ter
             if (desktopId == currentDesktop && lastActivatedTime > max)
             {
                 max = lastActivatedTime;
-                mostRecentWeak = w;
+                mostRecent = w;
             }
         }
-    }
-
-    // GetVirtualDesktopId(), as current implemented, should always return on the main thread.
-    _assertIsMainThread();
 
-    const auto mostRecent = mostRecentWeak.lock();
-    auto window = mostRecent.get();
-
-    if (!window)
+        // GetVirtualDesktopId(), as current implemented, should always return on the main thread.
+        _assertIsMainThread();
+        window = mostRecent.get();
+    }
+    else
     {
+        // If virtual desktops have never been used, and in turn Explorer never set them up,
+        // GetCurrentVirtualDesktopId will return false. In this case just use the current (only) desktop.
         window = _mostRecentWindow();
     }