Core dump when exiting

I'm running very simple sample code for testing.

When exiting externally via just closing the window, I get:

```
malloc_consolidate(): invalid chunk size
zsh: abort (core dumped) cargo run
```
Environment: Arch Linux, Sway (Wayland)

Code:
```rust

const HTML: &'static str = r#"

hello

"#;

fn main() {
let webview = web_view::builder()
.title("YouToo")
.content(web_view::Content::Html(HTML))
.size(800, 600)
.resizable(true)
.debug(true)
.user_data(0)
.invoke_handler(|webview, arg| {
match arg {
"reset" => {
//render(webview, *counter)?;
}
"exit" => {
webview.terminate();
}
_ => unimplemented!(),
};
Ok(())
})
.build()
.unwrap();

webview.run().unwrap();
}
```