window: solve crash problem.

Set destroy window in single function, to make window destroyed in message cycle thread.

src/anbox/platform/sdl/platform.cpp

@@ -298,11 +298,17 @@ void Platform::user_event_function(const SDL_Event &event) {
           window_manager_->remove_task(param->taskId);
         }
       } else if (event_type == USER_DESTROY_WINDOW) {
+        {
+          auto w = window_manager_->find_window_for_task(param->taskId);
+          if (w) {
+            w->destroy_window();
+          }
+        }
         window_manager_->erase_task(param->taskId);
         auto it = tasks_.find(param->taskId);
         if (it != tasks_.end()) {
-            windows_.erase(it->second);
-            tasks_.erase(it);
+          windows_.erase(it->second);
+          tasks_.erase(it);
         }
       }
       delete param;

src/anbox/platform/sdl/window.cpp

@@ -152,8 +152,13 @@ Window::Window(const std::shared_ptr<Renderer> &renderer,
   SDL_ShowWindow(window_);
 }
 
-Window::~Window() {
-  if (window_) SDL_DestroyWindow(window_);
+Window::~Window() {}
+
+void Window::destroy_window() {
+  if (window_) {
+    SDL_DestroyWindow(window_);
+    window_ = NULL;
+  }
 }
 
 bool Window::title_event_filter(int x, int y) {

src/anbox/platform/sdl/window.h

@@ -90,6 +90,7 @@ class Window : public std::enable_shared_from_this<Window>, public wm::Window {
   inline std::uint32_t get_property() {
       return visible_property;
   }
+  void destroy_window() override;
 
  private:
   static SDL_HitTestResult on_window_hit(SDL_Window *window, const SDL_Point *pt, void *data);

src/anbox/wm/window.h

@@ -65,6 +65,7 @@ class Window {
   std::string title() const;
   virtual bool checkResizeable() { return resizing_; }
   virtual void setResizing(bool resizing) { resizing_ = resizing; }
+  virtual void destroy_window() {}
  protected:
   graphics::Rect last_frame_;
   bool resizing_{false};