Fix CodeQL alert.

Author: kevinbackhouse

src/seclab_taskflow_agent/mcp_servers/codeql/jsonrpyc/__init__.py

@@ -749,7 +749,7 @@ def run(self) -> None:
             try:
                 line = self.rpc.stdin.readline()
             except IOError:
-                pass
+                line = None
 
             if line:
                 decoded_line = line.decode('utf-8').strip()