Fix agent reference (#2733)

plugins/rapid7_insight_agent/icon_rapid7_insight_agent/util/graphql_api/api_connection.py

@@ -338,6 +338,7 @@ def _get_agent(self, agent_input: str, agent_type: str, next_cursor: str = None)
         """
         start_time = datetime.now()
         agents = []
+        agent = None
         has_next_page = True
         if not next_cursor:
             payload = {