Fixed seg fault for observable modules

lib/qcd/observables/topological_charge.h

@@ -0,0 +1,49 @@
+/*************************************************************************************
+
+Grid physics library, www.github.com/paboyle/Grid
+
+Source file: ./lib/qcd/modules/topological_charge.h
+
+Copyright (C) 2017
+
+Author: Guido Cossu <guido.cossu@ed.ac.uk>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+See the full license in the file "LICENSE" in the top level distribution
+directory
+*************************************************************************************/
+/*  END LEGAL */
+
+#ifndef HMC_TOP_CHARGE_H
+#define HMC_TOP_CHARGE_H
+
+namespace Grid {
+namespace QCD (
+
+// this is only defined for a gauge theory
+template <class Impl>
+class TopologicalCharge : public HmcObservable<typename Impl::Field> {
+ private:
+  std::string Stem;
+
+ public:
+
+};
+
+)
+}
+
+#endif  //  HMC_TOP_CHARGE_H