cache also undefined values in option resolver (#9661)
cache also undefined values in option resolver (#9661)

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.
touletan/Chart.js,touletan/Chart.js,touletan/Chart.js,chartjs/Chart.js,touletan/Chart.js,nnnick/Chart.js,chartjs/Chart.js,chartjs/Chart.js,chartjs/Chart.js