Uncaught Error: "defaultExtended" is not a chart type.

If one extends default controller, i.e.:

`Chart.controllers.line.extend({ ... });`

then, following error is raised:

https://github.com/nagix/chartjs-plugin-style/blob/027eb2763c012ae013e1016f47e83a00938f7bbb/src/plugins/plugin.style.js#L54

