Fix KeyError exception triggered on closing a window (#2401)

Author: rchl

plugin/core/windows.py

@@ -545,7 +545,7 @@ def listener_for_view(self, view: sublime.View) -> Optional[AbstractViewListener
     def discard(self, window: sublime.Window) -> None:
         wm = self._windows.pop(window.id(), None)
         if wm:
-            wm.destroy()
+            sublime.set_timeout_async(wm.destroy)
 
 
 class RequestTimeTracker: