Fix adjoint vector size

[jblueh]

Proposed Changes

This PR fixes an issue in the discrete adjoint multizone driver where adjoints are seeded before sufficient adjoint vector size is guaranteed, resulting in an objective function gradient of zero.

The PR also contains other small fixes.

PR Checklist

• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).
• My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).
• I have added a test case that demonstrates my contribution, if necessary.
• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.