Duration fields with `0` are not saved / not reloaded

[romaintailhurat]

For Duration options "hours/minutes" and "years/months", the values are not saved / reloaded when getting back to a questionnaire if the values are 0.

To reproduce:

• create a question with a simple / duration answer type
• fill min or max with zeroes
• save & reload the questionnaires
• 💥 all the zeroes have disappear

[laurentC35]

Maybe in the code, 0 is equivalent to null and causes this issue

[romaintailhurat]

Fixed in 1.5.12-rc7-duration-0