Server won't run with port 0 (assigns any available port)

[ahtcx]

Describe the bug

On most systems, starting a server on port 0 will assign any available port. Vite does not allow to provide port 0, and will instead fall back to the default port 3000.

Reproduction

https://stackblitz.com/edit/vitejs-vite-g65k5l?file=vite.config.ts&terminal=dev

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/core instead.
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• The provided reproduction is a minimal reproducible example of the bug.

[ahtcx]

This can be fixed by using nullish coalescing here instead of the or operator.