Need safer way to check if a document has fields

[nonprofittechy]

I noticed a bug with the current way we detect whether the PDF has fields, which can happen with some oddly structured PDFs. The fix can be found in the Weaver, at this PR:

SuffolkLITLab/docassemble-ALWeaver#854

Here's a PDF that triggers this error:

motion_to_reconsider_civ_806-PDF with weird annotation.pdf