[Spine] Fix two color tint data not being copied across to backend buffer on first frame

[rh101]

Describe your changes

The two color tint vertex data was being updated after a new render command (TwoColorTrianglesCommand) is added, but the issue is that the addCommand method would have already updated the back-end buffer with the passed in data. This meant that the vertex data in the back-end buffer did not contain the updated values.

It's primarily an issue with TwoColorTrianglesCommand, because of how it works. The non-two color tint code uses TrianglesCommand, and does not seem to copy the data on addCommand, but rather hold a reference to the vertex data to be used later in the rendering process (if I understand it correctly). Regardless of that, the section for non-two color tint has also been changed to update the data before the Renderer::addCommand is called.

Issue ticket number and link

#1824

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[halx99]

cheers, thanks @rh101