eframe: add call to save_and_destroy in Exit event of run_return `EventResult::Exit` is hit before `Event::LoopDestroyed` is, and due to possibly some order of operations or drops the window is never destroyed on Linux. Adding a call to `winit_app.save_and_destroy();` where `EventResult::Exit` is checked solves this. Closes #2892 Signed-off-by: Luke D. Jones <luke@ljones.dev>