Panic if password script yields no password (#12)

This would happen, e.g., if the database is locked.

src/main.rs

@@ -226,25 +226,26 @@ async fn traverse(mut result: Multistatus, config: &Config) -> Result<bool, Box<
 
 #[tokio::main]
 async fn main() -> std::io::Result<()> {
-
     env_logger::Builder::from_env(Env::default()).init();
     println!("Publicise it!\n\n");
 
     let mut config = init().unwrap();
     if config.credentials.password == None {
         let output = Command::new(&config.credentials.password_script.as_ref().unwrap()).output().unwrap();
+        if output.stdout.len() == 0 {
+            panic!("[main] Failed to acquire password from provided script.");
+        }
         config.credentials.password = Some(String::from_utf8(output.stdout).unwrap());
     }
     debug!("[main] {:?}", &config);
+
     let full_path = &(String::from("/remote.php/dav/files/") + &config.credentials.username + "/" + &config.paths.target);
     let folder_contents: String =
         get_folder_contents(full_path, &config)
             .await
             .unwrap();
-
     let result: Multistatus = from_str(&folder_contents).unwrap();
     debug!("[main] {:?}", result);
-
     let _ = traverse(result, &config).await.unwrap();
     Ok(())
 }