115: Handle error case for SwapChain::get_next_texture r=kvark a=antonok-edm
Updates `SwapChain::get_next_texture` to account for https://github.com/gfx-rs/wgpu/pull/369. Otherwise, an invalid `Id` is returned and may cause confusing errors.
Co-authored-by: Anton Lazarev <antonok35@gmail.com>