Corrects boolean check for ignore_alpha variable.

[jamie-lemon]

In pymupdf_rag.py - we have the ignore_alpha variable defined as follows:

ignore_alpha: (bool, True) ignore text with alpha = 0 (transparent).

But then later:

parms.accept_invisible = (
            page_is_ocr(page) or ignore_alpha
        )  # accept invisible text

I think the logic here is to check if ignore_alpha is False is correct.

[jamie-lemon]

I'm reading this as "if we ignore alpha text (True) then that means we would ignore invisible text". Please let me know if my logic is flawed!