Support reading P mode TIFF images with padding

[radarhere]

Resolves #7995

[dwvisser]

This fixed the issue for me. In a fresh Python 3.8 virtualenv, I installed the branch:

pip install git+https://github.com/python-pillow/Pillow.git@bb2411dd01197d0a393dbcfdccfdd487a8c6d7be

Then this script ran, and output a usable PNG file:

from PIL import Image

image = Image.open("lorem_ipsum_90deg.tif")
image.save("output.png")
print("Done.")