[BUG] Deleting first slide causes user to view non-existing slide

[ssamikshaa]

Description
After deleting the first of two slides, the edit-dashboard displays a slide that does not exist.

To Reproduce
Steps to reproduce the behavior:

1. Add and view Dashboard
2. Click edit button on dashboard page
3. Create two new slides
4. Delete slide 1
5. Error: slide 2 of 1 is now displayed

Expected behavior
Edit dashboard should display slide 1 of 1.

Screenshots