InverseExposureLerp should return 1.0 when EYE_ADAPTION_DISABLED is 1

float InverseExposureLerp(float Exposure, float Alpha)
{
#if EYE_ADAPTATION_DISABLED
    return 1.0f;
#else
    // When Alpha=0.0, we want to multiply by 1.0. when Alpha = 1.0, we want to multiply by 1/Exposure.
    // So the lerped value is:
    //     LerpLogScale = Lerp(log(1),log(1/Exposure),T)
    // Which is simplified as:
    //     LerpLogScale = Lerp(0,-log(Exposure),T)
    //     LerpLogScale = -T * log(Exposure);    float LerpLogScale = -Alpha * log(Exposure);
    float Scale = exp(LerpLogScale);
    return Scale;
#endif
}