libecal: Move Due date relative to the Start date on a recurring task completion
When a recurring task has both start and due dates set, with the recurrence being applied to the start date, then completing the task will reset the due date to the start date.
For example a quarterly repeating report may only be started after the quarter has finished, but has to be completed every time until a certain due date with reminders attached.
Start Date: 01.04.2021
Due Date: 25.04.2021
Recurs: Every 3 months on the 1st day forever
On Completion the task is automatically changed to
Start Date: 01.07.2021
Due Date: 01.07.2021
Recurs: Every 3 months on the 1st day forever
Tested with 3.30.5 and 3.40.0.
Edited by Milan Crha