Infinite loop when adding to invalid dates.

[hermann-p]

When doing the following, I get an infinite loop:

const x = dayjs(null).businessDaysAdd(1);

This is probably due to the while loop in the businessDaysAdd method. It proceeds to the next day, reduces the days to add by one if that next day is a business day, and repeats until days to add reach zero.
When the starting date was invalid, no day will ever be a business day and the remaining days will never decrease.

My advice would be changing line 23 in index.js from

while (daysRemaining > 0) {

to something like

while (currentDay.isValid() && daysRemaining > 0) {

plus adding a test.