Fix edge case for custom angle on android devices

[orsenkucher]

With:

LiquidGlassSettings(
    thickness: 40,
    blur: 3,
    glassColor: context.colors.glassColor,
    chromaticAberration: 0.1,
    lightAngle: -math.pi / 4, // <- causes problem
    ambientStrength: 0.2,
    lightIntensity: 0.6,
)

I was getting black pixels on edge of glass on Android devices (iOS works fine):

Now we guard pow() and normalize() against zero inputs that produce NaN.

[orsenkucher]

Also orsenkucher@27448f8 is a good guard to have.