fix: remove file if download failed

Author: std-microblock

src/main.rs

@@ -384,6 +384,7 @@ impl Handler {
                                 let task = &mut tasklist[i_task];
                                 task.status = DownloadStatus::Failed;
                                 task.data = e.to_string();
+                                fs::remove_file(&current_task.dest);
                                 post_callback(&tasklist, "failed");
                                 return;
                             }