Bug: Removing expiry date for new transfer makes submission silently fail

[WebSpider]

Description

When preparing a new transfer on filesender 2.30, the submit button becomes non-functional when the date field is empty.

How to reproduce

Start a new transfer. Select the date-picker screen. Do not select a date, but empty the field. Complete the other input fields for the new transfer. Press the submit button. The submission fails silently.

Possible fix

Add some kind of hint for the user what is missing for the submission of the new transfer to succeed

[monkeyiq]

I guess we might also just make the date revert back to what it was if the user tries to empty the field.

[WebSpider]

That would work as well, if there is no valid date when the field loses focus, revert

[WebSpider]

This is not fixed in 2.31

[monkeyiq]

I see that the previous fix appeared to revert the value (on the upload page) but after the upload was complete the expires time was not set correctly looking in my transfers. The above #1289 should fix that.