frame.close() call with eframe on xorg not working if the main thread is still busy

**Describe the bug**
calling frame.close in the app while the main thread is still busy with something else will not close the ui.

**To Reproduce**
```rust
use std::sync::Barrier;

use eframe::egui;

fn main() {
let options = eframe::NativeOptions {
..Default::default()
};
let _ = eframe::run_native("App", options, Box::new(|_cc| Box::::default()));

let bar = Barrier::new(2);
bar.wait();
}

struct MyApp {}

impl Default for MyApp {
fn default() -> Self {
Self {}
}
}

impl eframe::App for MyApp {
fn update(&mut self, _ctx: &egui::Context, frame: &mut eframe::Frame) {
frame.close()
}
}
```

In this example i create an app that should close itself right after creation. At the same time the main thread is busy waiting for some event or doing something different.

**Expected behavior**
the app window should close and the main thread should continue working on whatever its currently up to.

**Desktop (please complete the following information):**
- OS: Linux Ubuntu
- With X11 / xorg

**Additional context**
this works on windows

Start by running the provided eframe::run_native example on Ubuntu with X11 and observe frame.close while the main thread waits on the Barrier. Trace the native window and event-loop handling for frame.close; done means the window closes while the main thread can continue, matching the reported Windows behavior.

Written by the indexing model from the issue text.