Fix empty variadic macros dropping LHS of token pasting

[hry-gh]

say you were wanting to do something like

#define MACRO_THAT_MAKES_A_VAR(var_name, var_type...) var##var_type/##var_name

/proc/foo()
  MACRO_THAT_MAKES_A_VAR(some_primitive) // var/some_primitive
  MACRO_THAT_MAKES_A_VAR(typed_var, /client) // /var/client/some_primitive

we currently drop the var from the expression, and would just emit /some_primitive