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.

src/basis_set/orbitalbasis_inc.F90

@@ -342,9 +342,13 @@ subroutine X(orbitalbasis_build)(this, namespace, ions, mesh, kpt, ndim, skip_s_
       os%ldorbs = max(pad_pow2(np), 1)
 
       call accel_create_buffer(os%X(buff_orb), ACCEL_MEM_READ_ONLY, R_TYPE_VAL, os%ldorbs*os%norbs) 
-      do iorb = 1, os%norbs
-        call accel_write_buffer(os%X(buff_orb), np, os%X(orb)(:, 1, iorb), offset = (iorb - 1)*os%ldorbs)
-      end do
+      ! In case we force the use of the submesh for X(orb) (for periodic systems), we do not want 
+      ! to write to X(buff_orb), as it has not the same size as X(orb) and will not be used anyway
+      if(.not. this%use_submesh .eqv. use_mesh) then
+        do iorb = 1, os%norbs
+          call accel_write_buffer(os%X(buff_orb), np, os%X(orb)(:, 1, iorb), offset = (iorb - 1)*os%ldorbs)
+        end do
+      end if
 
       if(this%use_submesh) then
         call accel_create_buffer(os%sphere%buff_map, ACCEL_MEM_READ_ONLY, TYPE_INTEGER, max(os%sphere%np, 1))