Fix incorrect scissor box in h2d.Scene.captureBitmap

[pkhead]

Currently, there is an issue with the OpenGL driver when using h2d.Scene.captureBitmap. When it sets the scissor bounds to the viewport bounds, GlDriver.curTexture incorrectly refers to the current texture rather than the texture being rendered into, causing the scissor box to potentially use an incorrect position. I will note that the DirectX driver has no problem here because it doesn't need to alter the scissor box if it's rendering to a texture, which the OpenGL driver needs to do.

I have fixed this by simply reordering some function calls in h2d.Scene.captureBitmap to ensure the correct framebuffer will be set when setRenderZone is called.

[ncannasse]

Maybe this should be fixed at the driver level @TothBenoit ;)

[pkhead]

imho I don't think its a driver issue, really. just in the captureBitmap function, setRenderZone was called when a framebuffer change hadn't yet been flushed to the driver. plus, OpenGL framebuffers are upside-down, whereas it seems DirectX framebuffers arent, so it is necessary to track the current framebuffer to see if the scissor box should be flipped; I also did the same thing when I wrote an OpenGL renderer for a project. But, I obviously am not the person who wrote all of this code, so I may be wrong.