gltf_viewer flickers on Metal when changing window size

[bejado]

Describe the bug Flickering inside of gltf_viewer when resizing the window with the Metal backend.

To Reproduce Steps to reproduce the behavior:

1. Run gltf_viewer --api metal
2. Resize the window until the model starts to flicker.

Bisected, issue started with 646dfa8b70235e9c242fe9e4c523f712ca78a388.

https://user-images.githubusercontent.com/5298046/183358193-f350563a-5f98-4df0-8180-504e128edfa9.mov