Radio simulations require N shower = 1

When running radio simulations with N showers > 1, I have the following error :

terminate called after throwing an instance of 'std::runtime_error'
  what():  ParquetStreamer not initialized. Either 1) add the corresponding module to the OutputManager, or 2) declare the module to write no output using NoOutput.
Aborted (core dumped)

In CORSIKA 7 radio simulations with multiple showers were not a feature but we could maybe make it a feature for C8.