fix intersection out of bounds point

[rcomer]

🚀 Pull Request

Description

Fixes #3391 I think. This addresses the very specific case where you request the entire 360 degrees, and one of the bounds is at the maximum/minimum threshold. Taking @valeriupredoi's example from #3391, you would still get that negative longitude point if you did something like cube.intersection(longitude=(0, 50)). I'm not sure that that makes sense but, looking at the tests, it appears to have been intentional.

I haven't added any extra comment to explain my logic, but I think it's covered by the existing:

iris/lib/iris/cube.py

Lines 3178 to 3180 in a9ae72f

	# being split. For bounds which may extend exactly the length of
	# the modulus, we simply preserve the point to bound difference,
	# and call the new bounds = the new points + the difference.

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[bjlittle]

@rcomer Hmmm you may have to re-open a new commit based on v3.0.x and cherry-pick out your commits onto it... or whatever is easiest.

As it stands, this PR is pulling unwanted master commits onto the v3.0.x release feature branch. Soz.

[rcomer]

😱

[rcomer]

@bjlittle see #4059