Omit empty filter log (#2393)

# Changes
#2354 collapsed these logs
into one but did not check that there was even an order filtered out.
This led to many logs stating that no order was filtered out for a given
reason.

crates/autopilot/src/solvable_orders.rs

@@ -605,7 +605,9 @@ impl OrderFilterCounter {
         for order_uid in filtered_orders.keys() {
             self.orders.remove(order_uid).unwrap();
         }
-        tracing::debug!(%reason, orders = ?filtered_orders, "filtered orders");
+        if !filtered_orders.is_empty() {
+            tracing::debug!(%reason, orders = ?filtered_orders, "filtered orders");
+        }
         filtered_orders.into_keys().collect()
     }