More descriptive coroutine exception error messages, more null checks in Level.Unload

Subsurface/Source/CoroutineManager.cs

@@ -93,7 +93,7 @@ namespace Barotrauma
 
                 catch (Exception e)
                 {
-                    DebugConsole.ThrowError("Coroutine " + Coroutines[i] + " threw an exception: " + e.Message);
+                    DebugConsole.ThrowError("Coroutine " + Coroutines[i].Name + " threw an exception: " + e.Message);
 
 #if DEBUG
                     throw e;

Subsurface/Source/Map/Levels/Level.cs

@@ -870,11 +870,20 @@ namespace Barotrauma
 
         private void Unload()
         {
-            if (renderer!=null) renderer.Dispose();
+            if (renderer!=null) 
+            {
+                renderer.Dispose();
                 renderer = null;
+            }
 
+            if (ruins != null)
+            {
                 ruins.Clear();
+                ruins = null;
+            }
 
+            if (wrappingWalls!=null)
+            {
                 for (int side = 0; side < 2; side++)
                 {
                     for (int i = 0; i < 2; i++)
@@ -883,10 +892,17 @@ namespace Barotrauma
                     }
                 }
 
+                wrappingWalls = null;
+            }
+
+
             cells = null;
             
+            if (bodies != null)
+            {
                 bodies.Clear();
                 bodies = null;
+            }
 
             loaded = null;
         }