[FIX] Gantt Chart: Fix incorrect saving of a Gantt chart having tasks with multiple dependencies to the database

When editing the Gantt chart by adding multiple dependencies to a task, multiple dependencies are saving back to database (from chart) without commas between dependencies. This result in, when the Gantt chart is reloaded, the dependencies don't work. I fixed this issue by adding a comma between dependencies before saving back to data database.

For more details, see : https://avan.tech/item71739 and https://dev.tiki.org/item7197