Bug 14949: (followup) Fix regression with hard due date

Bug 14949: (followup) Fix regression with hard due date

This patch fixes the regresseion as described in comment #3

To test:

- Go on smart-rules.pl and edit a line. Do not define a Hard due date, save.
  The value is "None defined".

- Edit the line, do not change anything and save.
  The value should be "None defined"

- Edit the line, define a hard due date, save.
  The date should display as expected.

- Edit the line agein, remove the hard due date, save.
  The value should be "None defined"

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Works as advertised

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>