Default-initialize RBJbase's state member
Default-initialize RBJbase's state member

The DllExport of RBJbase generates a default constructor,
Iir::RBJ::RBJbase::RBJbase(), which leaves RBJbase's state
member uninitialized.

Reported by @FeralChild64 on Gentoo Linux, AMD64, GCC 11.3.0:

iir1-1.9.3/iir/RBJ.h: In constructor 'constexpr
Iir::RBJ::RBJbase::RBJbase()':

iir1-1.9.3/iir/RBJ.h:66:26: warning:
   'Iir::RBJ::RBJbase::state' should be initialized in the
   member initialization list [-Weffc++] 66 | struct DllExport
   RBJbase : Biquad

berndporr/iir1,berndporr/iir1,berndporr/iir1,berndporr/iir1