[Docs Agent] Bug fix: Fix the "index out of range" issues in Docs Agent's chatbot web app.

[kyolee415]

Description of the change

This pull request fixes instances of the "index out of range" issues seen in Docs Agent's chatbot web app.

Motivation

Bug fix

Type of change

Choose one: (Bug fix)

Checklist

• [ X] I have performed a self-review of my code.
• [ X] I have added detailed comments to my code where applicable.
• [ X] I have verified that my change does not break existing code.
• [ X] My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• [ X] I am familiar with the Google Style Guide for the language I have coded in.
• [ X] I have read through the Contributing Guide and signed the Contributor License Agreement.