dynamicPublicPath option should consider using url.resolve for concatenation with publicPath

[elios264]

• Operating System: Windows
• Node Version: 12.x
• NPM Version: 6.9.0
• webpack Version: 4.35.2
• ${package} Version: 2.25.0

publicPath usually ends with a slash as in webpack docs:

The value of the option is prefixed to every URL created by the runtime or loaders. Because of this the value of this option ends with / in most cases.

so with this simple concatenation:

  if (overrides.dynamicPublicPath) {
    options.path = __webpack_public_path__ + options.path;
  }

we usually end up with double slash.

Expected Behavior

having only one slash web making request to middleware hmr

Actual Behavior

I'm having 2 slashes so hmr is broken

How Do We Reproduce?

setup up in webpack config:
'webpack-hot-middleware/client?dynamicPublicPath=true'
as entry point
set up
output: { publicPath: ${process.env.APP_URL}/, ... }