Fix some problem with ARPES output with spin-polarized calculations.
Description
Fix some problem with ARPES output with spin-polarized calculations. The calculation still does not give the correct result, but at least does not run out of the bounds of an array.
This is related to #687 .
Checklist
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I have checked that my code follows the Octopus coding standards -
I have added tests for all the new features added in this request.