fix(extract_thinker.markdown.markdown_converter): prevent using visio…

[glucard]

fix(extract_thinker.markdown.markdown_converter): prevent using vision (if set False) after using it as True

loader = DocumentLoaderPyPdf()
llm = LLM(model_name)
markdown_converter = MarkdownConverter(document_loader=loader, llm=llm)

markdown_converter.to_markdown(source_path, vision=True, pages=[1])
markdown_converter.to_markdown(source_path, vision=False, pages=[1]) # Before the fix, this was still executed as vision=True

[enoch3712]

Thank you!