fix: avoid crash with VAE tiling and certain image sizes

[wbruna]

I'm getting crashes with VAE tiling and specific image sizes, e.g. between 513 and 520.

./sd-cli --diffusion-model z_image_turbo-Q8_0_bf16.gguf --llm josiefied-qwen3-4b-abliterated-v2-q8_0.gguf -W 512 -H 520 --vae ae_bf16.safetensors --cfg-scale 1 --steps 2 -p forest --diffusion-fa --vae-tiling

ggml_extend.hpp:851: GGML_ASSERT(input_width % 2 == 0 && input_height % 2 == 0 && output_width % 2 == 0 && output_height % 2 == 0) failed

@stduhpf , I was able to avoid the crash by simply removing the assertion, but I'm not entirely sure whether it was triggered by a subtle bug elsewhere or if it's just no longer needed. The resulting images look fine.

Related to #1073 .

[stduhpf]

Hmm maybe that's a remain of the older tiling implementation.