stb_image: fix d1252e1bb9 for building in C

stb_image.h

@@ -6394,11 +6394,11 @@ static stbi_uc *stbi__process_gif_raster(stbi__context *s, stbi__gif *g)
 // two back is the image from two frames ago, used for a very specific disposal format
 static stbi_uc *stbi__gif_load_next(stbi__context *s, stbi__gif *g, int *comp, int req_comp, stbi_uc *two_back)
 {
-   STBI_NOTUSED(req_comp);
    int dispose; 
    int first_frame; 
    int pi; 
    int pcount; 
+   STBI_NOTUSED(req_comp);
 
    // on first frame, any non-written pixels get the background colour (non-transparent)
    first_frame = 0; 
@@ -6619,10 +6619,10 @@ static void *stbi__load_gif_main(stbi__context *s, int **delays, int *x, int *y,
 
 static void *stbi__gif_load(stbi__context *s, int *x, int *y, int *comp, int req_comp, stbi__result_info *ri)
 {
-   STBI_NOTUSED(ri);
    stbi_uc *u = 0;
    stbi__gif g;
    memset(&g, 0, sizeof(g));
+   STBI_NOTUSED(ri);
 
    u = stbi__gif_load_next(s, &g, comp, req_comp, 0);
    if (u == (stbi_uc *) s) u = 0;  // end of animated gif marker

stb_image_write.h

@@ -1090,11 +1090,11 @@ unsigned char *stbi_write_png_to_mem(const unsigned char *pixels, int stride_byt
       int filter_type;
       if (force_filter > -1) {
          filter_type = force_filter;
-         stbiw__encode_png_line(const_cast<unsigned char*>(pixels), stride_bytes, x, y, j, n, force_filter, line_buffer);
+         stbiw__encode_png_line((unsigned char*)(pixels), stride_bytes, x, y, j, n, force_filter, line_buffer);
       } else { // Estimate the best filter by running through all of them:
          int best_filter = 0, best_filter_val = 0x7fffffff, est, i;
          for (filter_type = 0; filter_type < 5; filter_type++) {
-            stbiw__encode_png_line(const_cast<unsigned char*>(pixels), stride_bytes, x, y, j, n, filter_type, line_buffer);
+            stbiw__encode_png_line((unsigned char*)(pixels), stride_bytes, x, y, j, n, filter_type, line_buffer);
 
             // Estimate the entropy of the line using this filter; the less, the better.
             est = 0;
@@ -1107,7 +1107,7 @@ unsigned char *stbi_write_png_to_mem(const unsigned char *pixels, int stride_byt
             }
          }
          if (filter_type != best_filter) {  // If the last iteration already got us the best filter, don't redo it
-            stbiw__encode_png_line(const_cast<unsigned char*>(pixels), stride_bytes, x, y, j, n, best_filter, line_buffer);
+            stbiw__encode_png_line((unsigned char*)(pixels), stride_bytes, x, y, j, n, best_filter, line_buffer);
             filter_type = best_filter;
          }
       }