title: Webpack optimization issue
body: <p>After migrating to webpack 4.16.0 i encountered issue.</p>
  
  <p>I have 2 entries defined like that</p>
  
  <pre><code>entry: {
    app: ['./src/app.js'],
    index: ['./src/index.js']
  },
  </code></pre>
  
  <p>And two html pages</p>
  
  <pre><code>new HtmlWebpackPlugin({
    template: './index.html',
    filename: './index.html',
    inject: 'head',
    title: 'Content Stream',
    chunks: ['index']
  }),
  new HtmlWebpackPlugin({
    template: './app.html',
    filename: './app.html',
    title: 'Content Stream',
    chunks: ['vendor', 'app']
  })
  </code></pre>
  
  <p>Using <code>webpack.optimization</code> (which work fine) </p>
  
  <pre><code>optimization: {
      splitChunks: {
        cacheGroups: {
          commons: {
            test: /[\\/]node_modules[\\/]/,
            name: 'vendor',
            chunks: 'all'
          }
        }
      }
    },
  </code></pre>
  
  <p>Code in bundle on <code>index</code> page is not executed until i add <code>vendor</code> chunk. But i don't need it there. </p>
  
  <p>I receive <code>index</code> chunk contents but looks like harmony modules inializing-running part is moved to <code>vendor</code></p>
  
  <p>So how to deal with this?</p>