BUG: when Docq doesn't know the answer it still references a source

[janaka]

Problem

When the LLM responds that it doesn't know the answer to the question a source(s) are still referenced.

At present sources seems to be listed based on what's retrieved rather than what was used in the answer.

Recreate

Create a new chat thread. upload a file. Ask a question that the file would not have the info about.

Desired Behaviour

• When the response states it doesn't know the answer, there shouldn't be any source referenced.
• Even when the answer is given, only the sources that were used in the answer should be listed.

[janaka]

The cause of this is most like that retrieval is returning nodes and they are blindly being referenced as sources. We probably need extra logic to not to render sources if the LLM response is borked.