Wgpu-rs: msaa-line example crashes on resize

[RazrFalcon]

> cargo run --release --example msaa-line
    Finished release [optimized] target(s) in 0.04s
     Running `target/release/examples/msaa-line`
thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `Some(Extent { width: 808, height: 602, depth: 1 })`,
 right: `Some(Extent { width: 800, height: 600, depth: 1 })`: Extent state must match extent from view', <::std::macros::panic macros>:5:6
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
[2020-06-01T19:33:44Z ERROR gfx_memory::heaps] Heaps still have 11 types live on drop
[2020-06-01T19:33:44Z ERROR gfx_memory::allocator::general] Memory leak: SizeEntry(8192000) is still used
[2020-06-01T19:33:44Z ERROR gfx_memory::allocator::general] Memory leak: SizeEntry(8273920) is still used
[2020-06-01T19:33:44Z ERROR gfx_memory::allocator::general] Memory leak: SizeEntry(2560) is still used
[2020-06-01T19:33:44Z ERROR gfx_memory::allocator::general] Memory leak: SizeEntry(16384) is still used
[2020-06-01T19:33:44Z ERROR gfx_memory::allocator::general] Memory leak: SizeEntry(131072) is still used

Running on Linux, KDE, nVidia.

[imjasonmiller]

I've encountered the same bug with b1f3fba on Linux, Arch, with an RX480.

[nilgoyette]

I tested v0.6 on Windows, resizing and maximizing, there's no crash.

[RazrFalcon]

Fixed.