fix checkbox icon update, add unique check on async tasks

src/main.cpp

@@ -1109,7 +1109,7 @@ LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wp, LPARAM lp)
             {
                 App::I->resize(w, h);
                 App::I->redraw = true;
-            });
+            }, true);
         }
         break;
     }