Fixed also for nonblocking backend

Author: GiovaGa

include/graphblas/nonblocking/blas2.hpp

@@ -499,6 +499,19 @@ namespace grb {
 				if( nnz( v ) < size( v ) ) {
 #ifdef _DEBUG
 					std::cout << "\t Dense descriptor given but input vector was sparse\n";
+#endif
+					return ILLEGAL;
+				}
+				if( nnz( u ) < size( u ) ) {
+#ifdef _DEBUG
+					std::cout << "\t Dense descriptor given but output vector was sparse\n";
+#endif
+					return ILLEGAL;
+				}
+				if( size( mask ) > 0 && nnz( mask ) < size( mask ) ) {
+#ifdef _DEBUG
+					std::cout << "\t Dense descriptor given but output mask has sparse "
+						<< "structure\n";
 #endif
 					return ILLEGAL;
 				}