Set Alambda = 0 and Akappa = 0 in case lambda = 0 or kappa = 0.

With the following SHLA NMSSM configuration an exception was thrown
and the writing of the SLHA file was incomplete:

Block EXTPAR  # Input parameters
   61   0.1                  # lambda
   65   65                   # lambda * <S>
   68   68                   # mu'