log backtrace when logging last_seen_index error

Author: syphar

src/utils/daemon.rs

@@ -31,7 +31,7 @@ pub fn watch_registry(
         Ok(None) => {}
         Err(err) => {
             log::error!(
-                "queue locked because of invalid last_seen_index_reference in database: {}",
+                "queue locked because of invalid last_seen_index_reference in database: {:?}",
                 err
             );
             build_queue.lock()?;