Assertion failure when rotating camera in glwindow

[jdm]

Rotate the camera left or right too far and you see:

assertion failed: self.is_normalized() (thread main, at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/euclid-0.20.3/src/rotation.rs:625)
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.38/src/backtrace/libunwind.rs:88
      backtrace::backtrace::trace_unsynchronized
             at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.38/src/backtrace/mod.rs:66
   1: backtrace::backtrace::trace
             at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.38/src/backtrace/mod.rs:53
   2: backtrace::capture::Backtrace::create
             at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.38/src/capture.rs:164
   3: backtrace::capture::Backtrace::new
             at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.38/src/capture.rs:128
   4: servo::main::{{closure}}
             at ports/glutin/main2.rs:142
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:472
   6: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:375
   7: rust_begin_unwind
             at src/libstd/panicking.rs:302
   8: std::panicking::begin_panic
   9: std::panicking::begin_panic
  10: euclid::rotation::Rotation3D<T,Src,Dst>::transform_point3d
             at /Users/jdm/src/webxr-master/webxr/<::core::macros::panic macros>:3
  11: euclid::rotation::Rotation3D<T,Src,Dst>::transform_vector3d
             at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/euclid-0.20.3/src/rotation.rs:656
  12: euclid::rigid::RigidTransform3D<T,Src,Dst>::post_transform
             at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/euclid-0.20.3/src/rigid.rs:122
  13: <webxr::glwindow::GlWindowDevice as webxr_api::device::Device>::wait_for_animation_frame
             at /Users/jdm/src/webxr-master/webxr/glwindow/mod.rs:129
  14: webxr_api::session::SessionThread<D>::handle_msg
             at /Users/jdm/src/webxr-master/webxr-api/session.rs:213
  15: <webxr_api::session::SessionThread<D> as webxr_api::session::MainThreadSession>::run_one_frame
             at /Users/jdm/src/webxr-master/webxr-api/session.rs:251
  16: webxr_api::registry::MainThreadRegistry<Swap>::run_one_frame
             at /Users/jdm/src/webxr-master/webxr-api/registry.rs:151
  17: compositing::compositor::IOCompositor<Window>::perform_updates
             at components/compositing/compositor.rs:1502
  18: servo::Servo<Window>::handle_events
             at components/servo/lib.rs:756
  19: servo::app::App::handle_events
             at ports/glutin/app.rs:204
  20: servo::app::App::run_loop
             at ports/glutin/app.rs:165
  21: servo::app::App::run
             at ports/glutin/app.rs:88
  22: servo::main
             at ports/glutin/main2.rs:170
  23: std::rt::lang_start::{{closure}}
             at /rustc/246be7e1a557b8ac8287c6842379a0db67770be6/src/libstd/rt.rs:61
  24: std::rt::lang_start_internal::{{closure}}
             at src/libstd/rt.rs:48
      std::panicking::try::do_call
             at src/libstd/panicking.rs:287
  25: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:80
  26: std::panicking::try
             at src/libstd/panicking.rs:265
      std::panic::catch_unwind
             at src/libstd/panic.rs:396
      std::rt::lang_start_internal
             at src/libstd/rt.rs:47
  27: std::rt::lang_start
             at /rustc/246be7e1a557b8ac8287c6842379a0db67770be6/src/libstd/rt.rs:61
  28: servo::main::{{closure}}