Ensure the OverlayStack is cleared when the app loop finishes.

src/musikbox/cursespp/App.cpp

@@ -230,6 +230,8 @@ void App::Run(ILayoutPtr layout) {
 
         MessageQueue::Instance().Dispatch();
     }
+
+    overlays.Clear();
 }
 
 void App::UpdateFocusedWindow(IWindowPtr window) {

src/musikbox/cursespp/OverlayStack.cpp

@@ -93,4 +93,8 @@ void OverlayStack::Remove(ILayout* layout) {
         setOverlayStack(*it, nullptr);
         this->stack.erase(it);
     }
+}
+
+void OverlayStack::Clear() {
+    this->stack.clear();
 }

src/musikbox/cursespp/OverlayStack.h

@@ -46,6 +46,10 @@ namespace cursespp {
             void Remove(ILayoutPtr layout);
             void Remove(ILayout* layout);
 
+        protected:
+            friend class App;
+            void Clear(); /* don't want this exposed to the public */
+
         private:
             std::vector<ILayoutPtr> stack;
     };