make protect math exit early for money

[zkamvar]

This adds a catch that will make the $protect_math() method exit early without an error if there is unbalanced math without any trailing dollar signs, which will indicate text with dollar amounts (like grants).

Note that this is still vulnerable if dollars are mixed with math that is broken across lines.

This will fix #121

[yabellini]

This is great! Thanks @zkamvar ! 🙏

[maelle]

Thank you!!