If I set server.host as true and server.open it doesn't work

[lubomirblazekcz]

Describe the bug

When I set server.host as true and have set open, it opens in browser as undefined:3000/index.html

Reproduction

export default {
    server: {
        host: true,
        open: "/index.html"
    },
}

System Info

  System:
    OS: macOS 11.3.1
    CPU: (8) x64 Apple M1
    Memory: 73.75 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 14.15.5 - ~/.nvm/versions/node/v14.15.5/bin/node
    Yarn: 1.22.10 - ~/.nvm/versions/node/v14.15.5/bin/yarn
    npm: 7.11.2 - ~/.nvm/versions/node/v14.15.5/bin/npm
  Browsers:
    Chrome: 90.0.4430.93
    Firefox: 88.0.1
    Firefox Developer Edition: 89.0
    Safari: 14.1
  npmPackages:
    vite: ^2.3.0 => 2.3.0