FIX: Don't show the Later This Week option in date pickers on Sundays (PR #13839)

Moment.js’ day() function returns 0 for Sunday. This is the same problem as in FIX: Don't show the This Weekend option in date pickers on Sundays by AndrewPrigorshnev · Pull Request #13838 · discourse/discourse · GitHub, but in this specific case I’m not 100% sure that we consider this as a bug.

It depends on what we consider as the first day of the week. If this it is Monday which is an international standard as I understand, then this is the bug, and we should merge this PR.