Fix Issue 945 - `ngx-select` doesn't react to zero option

[ruahung20011]

Summary

Replace me with a description of changes. Include screenshots where appropriate.

Checklist

• [ ] *Added unit tests
• [ ] *Added a code reviewer
• [x] Added changes to /projects/swimlane/ngx-ui/CHANGELOG.md under HEAD (Unreleased)
• [ ] Updated the demo page
• [ ] Included screenshots of visual changes

*required

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