[Bug] Virtual modules are rebuilt on any change

[non25]

Hi dear devs!

• I'd be willing to submit the fix

Describe the bug

Virtual modules are rebuilt on any change

To Reproduce

https://github.com/non25/webpack-virtual-modules-rebuild-repro

Environment if relevant (please complete the following information):

• Arch Linux latest
• Node version v14.9.0
• Webpack version v4.44.1

Additional context

Originally this was started in hopes to fix svelte-loader (which adapted this plugin) from reloading virtually generated css which on some setups could waste up to 40s of time on any change.

This issue and info could be relevant:
webpack/webpack#5824

Any insight is appreciated.