server: handle application/* as an attachment

server/src/bin/letterbox-server.rs

@@ -119,9 +119,10 @@ async fn download_attachment(
     } else {
         format!("id:{}", id)
     };
-    info!("download attachment {mid} {idx}");
+    info!("download attachment message id '{mid}' idx '{idx}'");
     let idx: Vec<_> = idx
         .split('.')
+        .filter(|s| !s.is_empty())
         .map(|s| s.parse().expect("not a usize"))
         .collect();
     let attachment = attachment_bytes(&nm, &mid, &idx)?;