fix: ensure modelIndex is always less than array length

[tnrdd]

Description

When switching between models in the media gallery sometimes modelIndex in GWCanvas is set to be the same length of the mediaGallery array and it address to an index of an undefined element, causing gwContent.raw.get() to error out and the media content carousel to be stuck on the same model before the click.

This make sure modelIndex is not off by one and it always wrap around when it would be less than zero or equal the length of the array.

Issue

fixes #57

Checklist:

• [x] My commit message follows the Conventional Commits specification
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have tested my code
• [x] My changes generate no new warnings
• [x] My PR is rebased off the most recent develop or appropriate feature branch
• [x] My PR is opened against the develop or appropriate feature branch

Alert Reviewers

@codynhat @gravenp

[codynhat]

I am still able to reproduce the original issue. It happens also when not at the end of the media gallery, and only when the objects are not cached.

[tnrdd]

I thought the freezing was only because of the out of bound access error but besides that when switching on first load the old model remained a second displayed while the name of the new model was already showing. It now should show a spinner until the new model is loaded.

[codynhat]

Looks good now!