GIF: unbounded frame count grows memory with no cap

Title: GIF: unbounded frame count grows memory with no cap

stbi__load_gif_main adds one layer per frame. layers has no upper bound. Each layer costs wh4 plus sizeof(int) for delays.

Repro (header as-is, ASan build): 100 frames 32x32, 2320 bytes on disk, loads z=100, 409600 bytes resident. 10000 frames 8x8, 230020 bytes on disk, loads z=10000, 2560000 bytes resident. 20000 frames 1x1, 460020 bytes on disk, loads z=20000.

Growth is linear. No warning.

Code: stb_image.h, stbi__load_gif_main, around line 6990. ++layers, then malloc/realloc(layersstride) and layerssizeof(int) with raw int math. w and h go through mad3sizes_valid. layers does not.

Past ~524288 frames at 32x32 the int wraps. I did not trigger that part here. I report DoS only.

Files to repro: generator in stb_gif_layers.cpp (makes minimal GIFs with N frames). Build with clang++ -fsanitize=address -I. against stb_image.h.