`matchGrowth()` gives error when there is no `w_inf` column

`matchGrowth()` is trying to be nice and tries to calculate the maturity age from von Bertalanffy parameters when `age_mat` is not supplied. Unfortunately it does this even if there is no `w_inf` column and this leads to an error message:
`Error in names(a_mat) <- sp$species : 
  'names' attribute [12] must be the same length as the vector [0]`