calendar: DateUtils: Fix regex check for date
According to MDN, if no match is found, String.prototype.match returns null,
not an empty array.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match
According to MDN, if no match is found, String.prototype.match returns null,
not an empty array.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match