Set HiDpiMode to Locked(1.0) cause invalid scissor rect on MacOS#62

<!--Thank you for filing this! Please provide as much information as possible to help us diagnose and fix the issue--> ## Description I change the HiDpiMode from Default to Locked(1.0) in the cube example, and add some dbg! on [dbg-hidpi-1.0](https://github.com/CurryPseudo/imgui-wgpu-rs/tree/dbg-hidpi-1.0) It crash with these log and backtrace: ```bash Finished dev [unoptimized + debuginfo] target(s) in 0.44s Running `target/debug/examples/cube` [examples/cube.rs:393] &size = PhysicalSize { width: 1600, height: 1200, } [0.533005 ERROR]()(no module): Unexpected varying type: Array { base: [1], size: Constant([5]), stride: 4 } [0.708039 ERROR]()(no module): Unexpected varying type: Array { base: [1], size: Constant([5]), stride: 4 } [src/lib.rs:542] &clip_off = [ 0.0, 0.0, ] [src/lib.rs:542] &clip_scale = [ 1.0, 1.0, ] [src/lib.rs:567] &scissors = ( 0, 0, 3200, 2400, ) [src/lib.rs:567] &scissors = ( 64, 79, 504, 492, ) wgpu error: Validation Error Caused by: In a RenderPass note: encoder = `<CommandBuffer-(0, 3, Metal)>` In a set_scissor_rect command Invalid ScissorRect parameters thread 'main' panicked at 'Handling wgpu errors as fatal by default', /Users/fate/.cargo/registry/src/github.com-1ecc6299db9ec823/wgpu-0.8.1/src/backend/direct.rs:1955:5 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` looks like that clip rect is bigger than frame size ## System Information <!--Version of imgui-wgpu-rs, information about your OS if relevant, your tech stack, etc.--> <img width="490" alt="image" src="https://user-images.githubusercontent.com/21034795/127446950-66f97fcc-69c2-4544-be61-8dcf579d7637.png">