Add checks to verify message is not empty before querying OpenAI

[verovaleros]

Description

Fixes #5

It adds simple checks to ensure we are not querying OpenAI with empty messages. Messages can be empty, but the prompt is still sent; therefore, the cost of the query remains. If the messages are empty, then do not query at all.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Run py tests manually and all passed
• Run automatic tests through GitHub CI

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings