Bug in computation of currents and charges for driven solves

[parrangoiz]

Description: A clear and concise description of what the bug is.

I ran a simple driven simulation of a CPW and looked at the results in Paraview; the $E$ and $B$ fields as well as the energy densities $U_E$ and $U_B$ all look exactly as expected, but $J_s$ and $Q_s$ look like gibberish which suggests a bug in the way these are being computed from the fields before being written to disk. See the attached screenshots of $\text{Re}(E_y)$ and $|\text{Re}(J_s)|$.

To reproduce: Please provide minimal example that reproduces the error. For existing
examples, please provide a link.

N/A but I imagine this should be reproducible using the CPW crosstalk example from the docs.

Error message: Paste the complete error message or log, if applicable.

None.

Environment: Any environment details, such as operating system, compiler, etc.