Summary:
Our date-guessing logic analyzes text in full looking for date parts.
This diff skip all that work when text is so long that we don't need to
consider it to be a valid date.
This is a quick fix. There are probably many other cases when we don't
need to try hard to parse arbitrary text as dates.
Test Plan: Added a fixture and test case that would trigger the error without the fix.
Reviewers: paulfitz
Subscribers: paulfitz
Differential Revision: https://phab.getgrist.com/D2992
