SDL GPU Metal iOS - changing render target when scissoring was enabled can cause crash

[kiddkaffeine]

When using SDL_GPU's Metal renderer on iOS, changing the render target if scissoring was recently enabled can cause a crash. If scissoring was just recently disabled, the render state may be not flushed and FNA3D may setScissorRect and Metal can be finicky about scissor rects outside the render target.

Changing ApplySampler() to ApplyState() in https://github.com/FNA-XNA/FNA/blob/master/src/Graphics/GraphicsDevice.cs#L916 fixes the problem, but this is heavy.