fix: null guard on assignees in orchestrator dispatch

hermes-sovereign/orchestrator/orchestrator.py

@@ -397,7 +397,7 @@ def assign_issue(repo, number, agent_name):
     if not result:
         return False
 
-    current = [a.get("login", "") for a in result.get("assignees", [])]
+    current = [a.get("login", "") for a in (result.get("assignees") or [])]
     if agent_name in current:
         print(f"    Already assigned to {agent_name}")
         return True