Fix KeyError on router error logging

[neubig]

• This change is worth documenting at https://docs.all-hands.dev/
• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below

End-user friendly description of the problem this fixes or functionality this introduces.

We were seeing this error in logs:

  File "/app/openhands/runtime/impl/action_execution/action_execution_client.py", line 407, in get_mcp_config
    if result['router_error_log']:
       ~~~~~~^^^^^^^^^^^^^^^^^^^^

This patch should fix it.

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:d1c1eee-nikolaik   --name openhands-app-d1c1eee   docker.all-hands.dev/all-hands-ai/openhands:d1c1eee

[pekosoG]

is this fix going to be auto-deployed? i saw the github actions building the ver 0.40.0 triggered out of this merge 👀