async_slave calls set_XXX_variables with empty data

[markaren]

At each time step, async_slave and pseudo_async_slave tries to call set_XXX_variables even when there is no data to set. Subsequently, inheriting classes as well as instances of cse::slave are tasked with checking the validity of the data passed to them. IMO, the functions should not be called in the first place. Ask someone to implement cse::slave and they will probably either not check the validity of the input data or throw an exception if the data is invalid!

What has been done for the current v1::fmu and v2::fmu implementations is that they just return. IMO, new implementations should not have to copy this approach.

[markaren]

I think it's safe to close this. It works as is, new slave implementations just have to be observant and validate the received input.