Fix OEP full - spin polarized case

Description

The OEP full was not taking the right occupations for the spin-polarized case.

News snippet

The OEP full was not taking the right occupations for the spin-polarized case.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

testsuite/optimal_control/06-zbr98.test

@@ -36,5 +36,5 @@ match ; Eigenvalue 2 ; GREPFIELD(static/info, '2   --', 3) ; -0.173229
 # This test seems to be unstable with more than one MPI process, converging to different solutions.
 Processors : 1
 Input: 06-zbr98.02-oct.inp
-Precision : 0.01
+Precision : 0.04
 match ; J1 1st iteration  ; GREPFIELD(opt-control/convergence, ' 1  ', 3) ; 0.99839827