enable undo savestate load in the gui

src/frontend/qt_sdl/main.cpp

@@ -2205,6 +2205,8 @@ void MainWindow::onLoadState()
         if (slot > 0) sprintf(msg, "State loaded from slot %d", slot);
         else          sprintf(msg, "State loaded from file");
         OSD::AddMessage(0, msg);
+
+        actUndoStateLoad->setEnabled(true);
     }
     else
     {