Rasterizer should always call EndFrame

[blasten]

This honors the public documentation anyways.

https://github.com/flutter/engine/blob/2b6c71c4d3ab9f94fa6d6260f2b302891dd0132c/shell/common/rasterizer.cc#L159

[NoamDev]

@blasten You should probably mark it as done:)

[github-actions]

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