GuideChimp doesn't start if step index is greater than steps number

[r-brown]

Describe the bug
GuideChimp doesn't start if step index is greater than steps number.

To Reproduce
Steps to reproduce the behavior:

1. Define 2 steps in the tour
2. Set start step as 0 or 1 => works

guideChimpAdventCalendar.start(1);

3. Set start step as 2 => dosn't work

guideChimpAdventCalendar.start(2);

Expected behavior
At least last step should be opened (e.g. - 1)