Don't try to generate a random seed for tables with no seed generator

[Eyal Rozenberg]

In bm_utils.c, we call the gen_seed() member function for every table we set_state() for. For SSBM this is null for the Date table; so - let's check for NULL in set_state() not not try calling a NULL function by mistake.

Credit goes to @t3rmin4t04 in his fork.