DDS decoder: zero mask triggers ZeroDivisionError in DdsRgbDecoder

[tylzh97]

What did you do?

from PIL import Image

with Image.open("poc.dds") as img:
    img.load()

What did you expect to happen?

Image.UnidentifiedImageError

What actually happened?

ZeroDivisionError: division by zero

What are your OS, Python and Pillow versions?

• OS: Ubuntu 22.04
• Python: 3.10.18
• Pillow: 12.0.0 (latest)

poc.zip

[radarhere]

I've created #9272, but it doesn't fix this by raising an UnidentifiedImageError. Instead, you end up with an RGBA image with 1 pixel of transparent black.