If there is no project name, default workbook name shall be "noname.wbk"

eeschema/sim/sim_plot_frame.cpp

@@ -1125,7 +1125,12 @@ void SIM_PLOT_FRAME::menuSaveWorkbookAs( wxCommandEvent& event )
     wxString defaultFilename = m_simulator->Settings()->GetWorkbookFilename();
 
     if( defaultFilename.IsEmpty() )
+    {
+        if( Prj().GetProjectName().IsEmpty() )
+            defaultFilename = wxT( "noname.wbk" );
+        else
             defaultFilename = Prj().GetProjectName() + wxT( ".wbk" );
+    }
 
     wxFileDialog saveAsDlg( this, _( "Save Simulation Workbook As" ), m_savedWorkbooksPath,
                             defaultFilename, WorkbookFileWildcard(),
@@ -1530,7 +1535,12 @@ bool SIM_PLOT_FRAME::canCloseWindow( wxCloseEvent& aEvent )
         wxFileName filename = m_simulator->Settings()->GetWorkbookFilename();
 
         if( filename.GetName().IsEmpty() )
+        {
+            if( Prj().GetProjectName().IsEmpty() )
+                filename.SetFullName( wxT( "noname.wbk" ) );
+            else
                 filename.SetFullName( Prj().GetProjectName() + wxT( ".wbk" ) );
+        }
 
         wxString msg = _( "Save changes to '%s' before closing?" );