fix(active-index): resets index if activeIndex doesn't exist

[NicholasLancey]

Description

We discovered an edge case where the activeIndex did not exist. This often happens if the amount of GalleryItems changes based on the viewport width.

Solution

Adds a check to see if the activeIndex exists, if it doesn't run the goToIndex() function and default to 0.

Note

Fixes #3

[andrewrubin]

I think we can lose the useEffect, and integrate this logic into the actual goToIndex function. That thing should be updated to be a bit more defensive anyway. Inside that function, maybe instead of just accepting that index is defined, let's first check that it's valid, and if not, set to zero.

I think with this useEffect solution, we'll still briefly get a warning, since side-effects run after the render phase.

[marlonmarcello]

Agree with this one, otherwise we'll always have to resort to this useEffect trick.

[NicholasLancey]

A bit of back and fourth with @andrewrubin on this one.

1. I've added a check to validate the index passed through to the goToIndex function. That's unrelated to the issue addressed in this PR.
2. I've moved the useEffect to the context. Unfortunately I can't think of another way for this to work - as the function needs to run every time items changes.

[andrewrubin]

Agreed, thanks for entertaining the idea though. Tested on my end and working. Here's a screencap where items changes at 768:

Screen.Recording.2023-09-21.at.5.44.18.PM.mp4

[andrewrubin]

Merging this one