Segmentation Fault in plutofilter_color_transform due to missing NULL pointer check

[Focing123]

Description
I have identified a Segmentation Fault (Crash) in the plutofilter library. The issue occurs when a plutofilter_surface_t structure is initialized with a NULL pixel buffer and passed to processing functions like plutofilter_color_transform.

Vulnerability Type
NULL Pointer Dereference (CWE-476).

Location
File: plutofilter.h
Line: 460 (inside plutofilter_color_transform)

Root Cause
The library macros (specifically PLUTOFILTER_GET_PIXEL) access the pixels array without verifying if the pointer is valid.

#define PLUTOFILTER_GET_PIXEL(surface, x, y) \
    ((surface).pixels[(y) * (surface).stride + (x)])

Steps to Reproduce
Compile the following C code with plutofilter.h:

#define PLUTOFILTER_IMPLEMENTATION
#include "plutofilter.h"
#include <stdio.h>


int main(void) {
    plutofilter_surface_t toxic_surface;
    toxic_surface.width = 100;
    toxic_surface.height = 100;
    toxic_surface.stride = 100;
    // The vulnerability: passing NULL as the pixel buffer
    toxic_surface.pixels = NULL; 

    // This triggers the crash
    plutofilter_color_transform_invert(toxic_surface, toxic_surface, 1.0f);
    return 0;
}

Crash Log (AddressSanitizer)

==128771==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000
    #0 0x55a670865a0b in plutofilter_color_transform plutofilter.h:460
    #1 0x55a67086734e in plutofilter_color_transform_invert plutofilter.h:513
SUMMARY: AddressSanitizer: SEGV plutofilter.h:460 in plutofilter_color_transform

Suggested Fix
Add a validation check at the start of public functions to ensure surface.pixels is not NULL.