fixed errror when vars of cnt begin declare with key contain "begin" (#7457)

### What problem does this PR solve?
fixed errror when vars of cnt begin  declare with key contain "begin"

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

agent/component/base.py

@@ -466,7 +466,7 @@ class ComponentBase(ABC):
         outs = []
         for q in sources:
             if q.get("component_id"):
-                if q["component_id"].split("@")[0].lower().find("begin") >= 0:
+                if "@" in q["component_id"] and q["component_id"].split("@")[0].lower().find("begin") >= 0:
                     cpn_id, key = q["component_id"].split("@")
                     for p in self._canvas.get_component(cpn_id)["obj"]._param.query:
                         if p["key"] == key: