core, pulse, modules: Fix undefined behavior with array subscript of invalid type

core, pulse, modules: Fix undefined behavior with array subscript of invalid type

From the NetBSD manual:

     The first argument of these functions is of type int, but only a very
     restricted subset of values are actually valid.  The argument must either
     be the value of the macro EOF (which has a negative value), or must be a
     non-negative value within the range representable as unsigned char.
     Passing invalid values leads to undefined behavior.

     --  ctype(3)