Using -lsrat 0 causes clEnqueueNDRangeKernel() -54

Program currently accepts lsrat equal to 0 and stores its value into dockpars.num_of_lsentities, which in turn is used to define the work-group size of LS kernel.

A work-group of size zero leads to OpenCL error code -54.

In master branch: https://git.esa.informatik.tu-darmstadt.de/docking/ocladock/blob/master/host/src/getparameters.cpp#L262

In fastergrad branch: https://git.esa.informatik.tu-darmstadt.de/docking/ocladock/blob/fastergrad/host/src/getparameters.cpp#L267