Infinite Request Pending on Uploading Large Multipart Files

**Expected Behavior**
When uploading a file larger than the allowed multipart file size limit (50 MB in this case), the server should promptly respond with an appropriate error message, such as "payload reached size limit", and the request should not be left pending indefinitely.

**Current Behavior**
When a file of size around 51 MB is uploaded, the server responds correctly with "payload reached size limit". However, if a much larger file, say around 200 MB, is uploaded, the request remains pending indefinitely, although a "Multipart error" is logged in the console.

```
[dependencies]
actix-web = "4.4"
actix-multipart = "0.6.1"
```

```rs
#[derive(Debug, MultipartForm)]
struct UploadForm {
owner: Text,

#[multipart(rename = "file")]
files: Vec,
}

#[post("/upload")]
async fn upload(MultipartForm(form): MultipartForm) -> Result {
let owner: &str = &form.creator;

log::info!("Uploading {} file(s) to {}", file_count, owner);

for f in form.files {
let path = format!("{}/{}", UPLOAD_DIR, f.file_name.unwrap());
log::info!("Saving to {path}");
f.file.persist(path).unwrap();
}

Ok(HttpResponse::Ok().body("File uploaded."))
}

#[get("/")]
async fn index() -> Result {
let html = r#"
Upload Test




Submit


"#;

Ok(HttpResponse::Ok().body(html))
}

fn handle_multipart_error(err: MultipartError, req: &HttpRequest) -> Error {
log::error!("Multipart error: {}", err);

return Error::from(err);
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
env_logger::init_from_env(env_logger::Env::new().default_filter_or("info"));

log::info!("Starting HTTP server at {}:{}", HOST, PORT);

HttpServer::new(move || {
App::new()
.wrap(Logger::default())
.app_data(
MultipartFormConfig::default()
.total_limit(50 * 1024 * 1024) // 50 MB
.memory_limit(10 * 1024 * 1024) // 10 MB
.error_handler(handle_multipart_error),
)
.service(index)
.service(upload)
})
.workers(2)
.bind((HOST, PORT))?
.run()
.await
}

```

Start by reproducing the large-upload case with the shown upload entry point and MultipartFormConfig limits, then inspect multipart error handling around handle_multipart_error. Compare the 51 MB and 200 MB behaviors and trace why the request remains pending after the logged Multipart error. Done means oversized multipart uploads return an error promptly instead of remaining pending.

由索引模型根据 Issue 内容生成。