_calculate_scaling_factor doesn't work right when crop == 'noop'

[zackw]

As requested, I am re-filing bug #407, which was closed despite the buggy code not having changed at all.

sorl-thumbnail/sorl/thumbnail/engines/base.py

Lines 67 to 70 in eb17128

	def _calculate_scaling_factor(self, x_image, y_image, geometry, options):
	crop = options['crop']
	factors = (geometry[0] / x_image, geometry[1] / y_image)
	return max(factors) if crop else min(factors)

The image will be scaled to max(factors) when crop is noop, which is incorrect. crop being set to noop is documented to scale the image the same as if crop had been unset (https://sorl-thumbnail.readthedocs.io/en/latest/template.html#crop)

Suggested change:

def _calculate_scaling_factor(self, x_image, y_image, geometry, options):
    crop = options['crop']
    factors = (geometry[0] / x_image, geometry[1] / y_image)
    if not crop or crop == 'noop':
        return min(factors)
    else:
        return max(factors)

[camilonova]

@zackw looks good to me, please send a PR with a test. I'll be happy to merge it.

[zackw]

Will do. Might be a couple weeks before I get to it, please remind me if it gets to be March and you haven't heard from me.