stdlib: Fix 'nozero' for Scalar SimStats (#972)

When the `statistics::nozero` flag is set gem5 does not output that stat
if its value is zero. This was not the case for SimStats which output in
this case. This patch correct this behavior.

src/python/pybind11/stats.cc

@@ -145,6 +145,9 @@ pybind_init_stats(py::module_ &m_native)
         .def_property_readonly("flags", [](const statistics::Info &info) {
                 return (statistics::FlagsType)info.flags;
             })
+        .def_property_readonly("is_nozero", [](const statistics::Info &info) {
+                return info.flags.isSet(statistics::nozero);
+            })
         .def("check", &statistics::Info::check)
         .def("baseCheck", &statistics::Info::baseCheck)
         .def("enable", &statistics::Info::enable)