Crash when running vignette

[useobjc]

Reproduce step:

1. Run FilterShowcase example
2. Select Vignette filter

Then, app will crash with next exception:

validateFunctionArguments:3485: failed assertion `Fragment Function(vignetteFragment): 
argument uniform[0] from buffer(1) with offset(0) and length(40) has space for 40 bytes, but argument has a length(48).'

[tianye2856]

I have the same problem.

[agorskih]

Hi. There is some problem with sending VignetteUniform to the Vignette shader. To quick fix and run sample you can change Vignette.metal file.

typedef struct {
    float3 vignetteCenter;
    float3 vignetteColor;
    float vignetteStart;
    float vignetteEnd;
    float2 junk_padding; # <-- Add this line
} VignetteUniform;

[BradLarson]

This should be fixed as of #91