Skip empty batch

src/fetch.rs

@@ -55,6 +55,7 @@ impl FetchQueue {
         while let Some(q) = q_lock.pop_front() {
             batch.push(q);
         }
+        if batch.len() > 0 {
             let filters: Vec<Filter> =
                 batch.iter().map(move |x| Self::nip19_to_filter(&x.request).unwrap()).collect();
 
@@ -71,6 +72,7 @@ impl FetchQueue {
                 }
             }
         }
+    }
 
     fn nip19_to_filter(filter: &Nip19) -> Option<Filter> {
         match filter {