Fixed nullref when exiting the flight scene when surface thrust to weight readout enabled.
Fixed nullref when exiting the flight scene when surface thrust to weight readout enabled.

--- a/KerbalEngineer/Flight/Readouts/Vessel/SurfaceThrustToWeight.cs
+++ b/KerbalEngineer/Flight/Readouts/Vessel/SurfaceThrustToWeight.cs
@@ -1,7 +1,7 @@
 // 
 //     Kerbal Engineer Redux
 // 
-//     Copyright (C) 2014 CYBUTEK
+//     Copyright (C) 2016 CYBUTEK
 // 
 //     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
@@ -12,55 +12,41 @@
 //     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, see <http://www.gnu.org/licenses/>.
-// 
-
-#region Using Directives
-
-using System;
-
-using KerbalEngineer.Flight.Sections;
-
-#endregion
+//  
 
 namespace KerbalEngineer.Flight.Readouts.Vessel
 {
+    using System;
+    using Sections;
+
     public class SurfaceThrustToWeight : ReadoutModule
     {
-        #region Fields
-
-        private string actual = string.Empty;
-        private double gravity;
-        private string total = string.Empty;
-
-        #endregion
-
-        #region Constructors
+        private string m_Actual = string.Empty;
+        private double m_Gravity;
+        private string m_Total = string.Empty;
 
         public SurfaceThrustToWeight()
         {
-            this.Name = "Surface Thrust to Weight Ratio";
-            this.Category = ReadoutCategory.GetCategory("Vessel");
-            this.HelpString = "Shows the vessel's surface thrust to weight ratio.";
-            this.IsDefault = true;
+            Name = "Surface Thrust to Weight Ratio";
+            Category = ReadoutCategory.GetCategory("Vessel");
+            HelpString = "Shows the vessel's surface thrust to weight ratio.";
+            IsDefault = true;
         }
-
-        #endregion
-
-        #region Methods: public
 
         public override void Draw(SectionModule section)
         {
-            if (!SimulationProcessor.ShowDetails)
+            if (FlightGlobals.currentMainBody == null || SimulationProcessor.LastStage == null ||
+                !SimulationProcessor.ShowDetails)
             {
                 return;
             }
-            this.gravity = FlightGlobals.currentMainBody.gravParameter / Math.Pow(FlightGlobals.currentMainBody.Radius, 2);
-            this.actual = (SimulationProcessor.LastStage.actualThrust / (SimulationProcessor.LastStage.totalMass * this.gravity)).ToString("F2");
-            this.total = (SimulationProcessor.LastStage.thrust / (SimulationProcessor.LastStage.totalMass * this.gravity)).ToString("F2");
-            this.DrawLine("TWR (Surface)", this.actual + " / " + this.total, section.IsHud);
+
+            m_Gravity = FlightGlobals.currentMainBody.gravParameter / Math.Pow(FlightGlobals.currentMainBody.Radius, 2);
+            m_Actual = (SimulationProcessor.LastStage.actualThrust / (SimulationProcessor.LastStage.totalMass * m_Gravity)).ToString("F2");
+            m_Total = (SimulationProcessor.LastStage.thrust / (SimulationProcessor.LastStage.totalMass * m_Gravity)).ToString("F2");
+            DrawLine("TWR (Surface)", m_Actual + " / " + m_Total, section.IsHud);
         }
 
         public override void Reset()
@@ -72,7 +58,5 @@
         {
             SimulationProcessor.RequestUpdate();
         }
-
-        #endregion
     }
 }