[Fitting] Fix error in GLSDer::geomVar() function

Ponca/src/Fitting/gls.hpp

@@ -4,6 +4,7 @@
  file, You can obtain one at http://mozilla.org/MPL/2.0/. 
 */
 
+#include "Ponca/src/Fitting/enums.h"
 template < class DataPoint, class _WFunctor, typename T>
 inline FIT_RESULT
 GLSParam<DataPoint, _WFunctor, T>::finalize()
@@ -91,10 +92,10 @@ GLSDer <DataPoint, _WFunctor, DiffType, T>::geomVar(  Scalar wtau,
                                                       Scalar weta,
                                                       Scalar wkappa ) const
 {
-    static_assert( Base::isScaleDer, "Scale derivatives are required to compute Geometric Variation" );
-    Scalar dtau   = Base::dtau_normalized().col(0)(0);
-    Scalar deta   = Base::deta_normalized().col(0).norm();
-    Scalar dkappa = Base::dkappa_normalized().col(0)(0);
+    static_assert( bool(DiffType & FitScaleDer), "Scale derivatives are required to compute Geometric Variation" );
+    Scalar dtau   = dtau_normalized().col(0)(0);
+    Scalar deta   = deta_normalized().col(0).norm();
+    Scalar dkappa = dkappa_normalized().col(0)(0);
 
     return wtau*dtau*dtau + weta*deta*deta + wkappa*dkappa*dkappa;
 }