Fix in MatButterfly missing default ctor call needed for a proper ini.

It fixes a bug in MatButterfly<FPP, GPU2>::clone (cf.  test_matbutterfly_gpu.cpp.in)

src/faust_linear_operator/GPU2/faust_MatButterfly_gpu.h

@@ -27,7 +27,7 @@ namespace Faust
 			{
 			}
 
-			MatButterfly(const MatButterfly<FPP, GPU2>& bmat)
+			MatButterfly(const MatButterfly<FPP, GPU2>& bmat) : MatButterfly()
 			{
 				*this = bmat;
 			}