Fix bgfx demo

[Protoxy22]

I'm not 100% sure about the code, but at least the bgfx demo works again (tested on Windows)

[Spasi]

Hey @Protoxy22,

Thanks for the patch! The new code is fine and the old code is indeed not working. However, it looks like there's a relative recent bgfx bug that broke it:

bkaradzic/bgfx@72cbe83#diff-75ed10dd2a2698c8707c9c9750ec40b3d12bbdf747f0c18514ed89caa3b2c522L1881

Should have kept the other memCopy, that copies from g_platformData to m_init.platformData. I'm currently building bgfx with a fix, it will be available in the next 3.3.4 snapshot.

[Spasi]

Ended up with a different fix, but I can verify that the issue is resolved with the latest bgfx build and the original code. You can download the fixed build from https://www.lwjgl.org/browse/nightly.