If there is no task_id, do not generate a task link

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

playbooks/roles/flag_build_commits/files/flag_commit_build.py

@@ -46,6 +46,9 @@ def _koji_link(msg):
     if msg['request'] and '.stg.' in msg['request'][0]:
         base = "https://koji.stg.fedoraproject.org/koji"
 
+    if not msg["task_id"]:
+        return ''
+
     return base + "/taskinfo?taskID=%i" \
         % (msg['task_id'])