Fix a few issue in simulation (noticeable only when the calculation time is high):

- Wait for end of simulation before return from "C" locale to current locale
(to avoid data files created by ngspice using curr locale instead of "C" locale)
- Do not allow changing signal list to plot during simulation calculation
(avoid crashes)

eeschema/sim/sim_plot_frame.cpp

@@ -1336,6 +1336,12 @@ void SIM_PLOT_FRAME::onSettings( wxCommandEvent& event )
 
 void SIM_PLOT_FRAME::onAddSignal( wxCommandEvent& event )
 {
+    if( IsSimulationRunning() )
+    {
+        DisplayInfoMessage( this, _( "Simulator is running. Try later" ) );
+        return;
+    }
+
     SIM_PLOT_PANEL* plotPanel = CurrentPlot();
 
     if( !plotPanel || !m_exporter || plotPanel->GetType() != m_exporter->GetSimType() )
@@ -1354,6 +1360,12 @@ void SIM_PLOT_FRAME::onProbe( wxCommandEvent& event )
     if( m_schematicFrame == NULL )
         return;
 
+    if( IsSimulationRunning() )
+    {
+        DisplayInfoMessage( this, _( "Simulator is running. Try later" ) );
+        return;
+    }
+
     m_schematicFrame->GetToolManager()->RunAction( EE_ACTIONS::simProbe );
     m_schematicFrame->Raise();
 }