Fix a segfault for the excited state output in presence of frozen orbitals.

Description

Fix a segfault for the excited state output in presence of frozen orbitals.

Thanks to Vu Ngoc Tuoc for reporting this.

In the process of adding more tested outputs, I found that the velocity output was not working in MPI. This is also fixed in this merge request.

News snippet

Fix a segfault for the excited state output in presence of frozen orbitals.

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.