fix vignette operation crash issue

[suzp1984]

Reason: Fragment Uniform buffer alignment issue.

typedef struct {
    float2 vignetteCenter;
    float3 vignetteColor;
    float vignetteStart;
    float vignetteEnd;
} VignetteUniform;

this struct occupies 48 bytes, with the last 8 bytes useless.

the similar crash happens for zoom blur, bulge distortion, pinch distortion, sphere refraction, glass crash.