Vulkan: Non-directional lights with size > 0 shining on material with zero roughness results in broken specular lobes

[atirut-w]

Related to #68464.

Godot version

v4.0.alpha16.official [86dd3f3]

System information

Arch Linux, Vulkan Clustered, Nvidia 1660(Nvidia open driver 515.65.01-11)

Issue description

Note: issue is more visible when the camera is close to the specular lobes.

Steps to reproduce

1. Add a mesh and assign it a material with zero roughness. Currently only tested with a sphere.
2. Add an omnilight with size > 0 and shine it on the mesh

Minimal reproduction project

Lighting problem.zip

[Calinou]

There's likely a NaN or infinite value being generated as a result of a division by zero or something similar in the shader.