FPS sometimes undefined on the result

[bergden]

My colleague got the following result (Ubuntu):

{
  "gpu": "google, swiftshader device (subzero) (0x0000c0de), swiftshader driver (ANGLE (Google, Vulkan 1.3.0 (SwiftShader Device (Subzero) (0x0000C0DE)), SwiftShader driver))",
  "isMobile": false,
  "tier": 1,
  "type": "FALLBACK"
}

Our code didn't handle correctly cases where fps is undefined - is this expected behavior?
I can open a PR to document or add fps: -1 or something like that - but wanted to know if this is a supported case.