Fix drawing a rounded rectangle

[carolhmj]

Related issue: https://forum.babylonjs.com/t/potential-regression-in-bjs-5-21-0-failed-to-execute-arc-on-canvasrenderingcontext2d/33455
Related playground: https://playground.babylonjs.com/#R6NPW8

[azure-pipelines]

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[azure-pipelines]

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