Hoist untested branch in window

If there were unit tests for this function, the author would have
written it this way to make their own life easier.

src/window.rs

@@ -45,12 +45,9 @@ fn find_next_missing(
     recycler: &BlobRecycler,
     consumed: u64,
     received: u64,
-) -> Option<Vec<(SocketAddr, Vec<u8>)>> {
-    if received <= consumed {
-        return None;
-    }
+) -> Vec<(SocketAddr, Vec<u8>)> {
     let mut window = window.write().unwrap();
-    let reqs: Vec<_> = (consumed..received)
+    (consumed..received)
         .filter_map(|pix| {
             let i = (pix % WINDOW_SIZE) as usize;
 
@@ -70,8 +67,7 @@ fn find_next_missing(
             }
             None
         })
-        .collect();
-    Some(reqs)
+        .collect()
 }
 
 fn calculate_highest_lost_blob_index(num_peers: u64, consumed: u64, received: u64) -> u64 {
@@ -131,7 +127,12 @@ fn repair_window(
         consumed,
         received,
     );
-    if let Some(reqs) = find_next_missing(window, crdt, recycler, consumed, highest_lost) {
+
+    if received <= consumed {
+        return None;
+    }
+
+    let reqs = find_next_missing(window, crdt, recycler, consumed, highest_lost);
     inc_new_counter_info!("streamer-repair_window-repair", reqs.len());
     if log_enabled!(Level::Trace) {
         trace!(
@@ -148,9 +149,6 @@ fn repair_window(
         }
     }
     Some(reqs)
-    } else {
-        None
-    }
 }
 
 fn add_block_to_retransmit_queue(