Make sure at least one TFSF tangential dimension is nonzero

[momchil-flex]

@QimingFlex could you help add a validation for this since it led to a user error.

I think the nontrivial part is that you need to look at the intersection between the simuation domain and the TFSF box. Because otherwise you could have a source that is 1D and a simulation that is e.g. 2D but their intersection is 0D.

[QimingFlex]

I will look into it!

[QimingFlex]

@momchil-flex TFSF already has a _volume_validator that throws an error if any dimensions equal 0. Could you elaborate more on the problem?

[momchil-flex]

I think the issue might then only arise if someone puts a TFSF in a 1D simulation, i.e. simulation size 0 along both of the TFSF tangential directions.