Code coverage for DayPickerInput component

[JuhQ]

It seems that there is a if block which is not covered by the tests:

https://github.com/gpbl/react-day-picker/blob/master/src/DayPickerInput.js#L460-L467

That return is never reached in tests: https://codecov.io/gh/gpbl/react-day-picker/src/master/src/DayPickerInput.js#L466

I spent some time trying to add a test for this but I failed horribly :(