cache also undefined values in option resolver

[Flupp]

Otherwise, repeated lookups of undefined properties always trigger the
comparatively expensive resolution. This can be the case for example in
_calculateBarIndexPixels() in controller.bar.js when looking up
options.skipNull and options.maxBarThickness, which is done for each bar
in a bar chart.

[kurkle]

Just a quick check, can you test if https://www.chartjs.org/docs/latest/samples/line/segments.html sample works after this change?

I was probably thinking it should not be cached because of the fallback. But looks like all the tests pass, so I could have been wrong.

[Flupp]

Just a quick check, can you test if https://www.chartjs.org/docs/latest/samples/line/segments.html sample works after this change?

With the patch, the diagram seems to look and behave the same as before.

I was probably thinking it should not be cached because of the fallback. But looks like all the tests pass, so I could have been wrong.

I do not know how the option resolver works in detail. I assumed that the underlying configs do not change – at least not without invalidating the cache. With this assumption, I do not see a difference in caching defined or undefined values.

[kurkle]

Ran this on the uPlot bench data (and bar chart):

10 runs done in 19171ms. Average: 1917ms, min: 1862ms, max: 2027ms, variation: 165ms

vs master:

10 runs done in 21973ms. Average: 2197ms, min: 2105ms, max: 2466ms, variation: 361ms