feat(smart-contracts): owners count excludes the zero address

[clemsos]

Description

When a key is transferred to the zero address, the counter of unique owner should decrease

Issues

Fixes #13685 Refs #

Checklist:

• [ ] 1 PR, 1 purpose: my Pull Request applies to a single purpose
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have updated the docs to reflect my changes if applicable
• [ ] I have added tests (and stories for frontend components) that prove my fix is effective or that my feature works
• [ ] I have performed a self-review of my own code
• [ ] If my code involves visual changes, I am adding applicable screenshots to this thread

Release Note Draft Snippet

[julien51]

Thanks! Also I think we should make it possible for the zero address to own more than the limit of token per address?

[clemsos]

Thanks! Also I think we should make it possible for the zero address to own more than the limit of token per address?

Yep, addressed in 5f4de96 -- fix #14837