Fix bugs when using the server option together with different client/server URLs

[hedgepigdaniel]

This PR contains a:

• [x] bugfix
• [ ] new feature
• [ ] code refactor
• [ ] test update
• [ ] typo fix
• [ ] metadata update

Motivation / Use-Case

Having a different browser address and server address is useful if there is a proxy in between. The server option is useful because it removes the need to have two servers and two ports.

There are two bugs fixed:

• The validation code previously rejected a configuration such as this:

{
  host: {
    client: 'someurl',
  },
  port: {
    client: 80
  },
  server,
}

even though the provided server is already listening on a host/port

• When the server option was used, the client ignored the host.client setting

Breaking Changes

None

Additional Info

[aaronup]

Can we get this merged? this would be super helpful

[hedgepigdaniel]

You would be better off asking here: https://github.com/shellscape/webpack-hot-client

[hedgepigdaniel]

Or use my fork, webpack-hmr-client