Handle lua -> C# function invocation exceptions more gracefully

Upsilon/BaseTypes/LuaFunction.cs

@@ -75,7 +75,16 @@ namespace Upsilon.BaseTypes
                     objects.Add(null);
                 }
             }
+
+            try
+            {
                 return method.Invoke(_object, objects.ToArray()).ToLuaType();
             }
+            catch (TargetInvocationException e)
+            {
+                if (e.InnerException != null) throw e.InnerException;
+                throw;
+            }
+        }
     }
 }