Tracker: close Desktop window on switch to spatial mode

If you have the Desktop window open when you switch to spatial
mode this will now close the window. You aren't allowed to have
the Desktop open in 2 places symultaneously in spatial mode.

src/kits/tracker/ContainerWindow.cpp

@@ -1674,6 +1674,14 @@ BContainerWindow::MessageReceived(BMessage* message)
 							SetPathWatchingEnabled(settings.ShowNavigator()
 								|| settings.ShowFullPathInTitleBar());
 						}
+
+						if (!settings.SingleWindowBrowse()
+							&& dynamic_cast<BDeskWindow*>(this) == NULL
+							&& TargetModel()->IsDesktop()) {
+							// close the "Desktop" window, but not the Desktop
+							this->Quit();
+						}
+
 						SetSingleWindowBrowseShortcuts(
 							settings.SingleWindowBrowse());
 						break;