Allow ImageOps.contain() to create zero dimension images

[radarhere]

ImageOps.contain() attempts to fits an image within a certain size. If those calculations end up with an image where one dimension is zero, then an error is currently raised.

>>> from PIL import Image, ImageOps
>>> im = Image.new("1", (1, 10))
>>> ImageOps.contain(im, (5, 5))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "PIL/ImageOps.py", line 300, in contain
    return image.resize(size, resample=method)
  File "PIL/Image.py", line 2430, in resize
    im = self.im.resize(size, resample, box)
ValueError: height and width must be > 0

This PR suggests allowing zero dimension images to be created. It is an alternative to #9672, which forces the image to be at least 1px wide or high.