simplify condition for computing m_exp_data

Sim/Fitting/SimDataPair.cpp

@@ -100,8 +100,10 @@ void SimDataPair::execSimulation(const mumufit::Parameters& params)
     m_sim_data = std::make_unique<Datafield>(simulation->simulate());
     ASSERT(!m_sim_data->empty());
 
-    if (m_exp_data && !m_exp_data->empty() && m_uncertainties && !m_uncertainties->empty())
+    if (m_exp_data) {
+        ASSERT(!m_exp_data->empty());
         return;
+    }
 
     auto* const sim2d = dynamic_cast<ScatteringSimulation*>(simulation.get());
     if (sim2d)