Datepicker: beforeShowDay is passed wrong date when dayNamesShort are used

[pramodjodhani]

👋

I had raised a similar issue previously #1971, which was for "D M d yy" format. I have found that the same problem happens with dd. MM yy format too.

Please check this minimal example to recreate the problem.: https://jsfiddle.net/smnt1o5r/2/

Please note that the dates passed to the callback function are of 2031, which is very random

I also noticed that this time the problem is not dependent on dayNamesShort