Fix debug assert issue with vtable methods.

Author: tritao

src/AST/ClassLayout.cs

@@ -31,14 +31,7 @@ public struct VTableComponent
         public Declaration Declaration;
 
         /// Method declaration (if Kind == FunctionPointer).
-        public Method Method
-        {
-            get
-            {
-                Debug.Assert(Kind == VTableComponentKind.FunctionPointer);
-                return Declaration as Method;
-            }
-        }
+        public Method Method => Declaration as Method;
     }
 
     /// <summary>

src/Generator/AST/VTables.cs

@@ -34,6 +34,7 @@ private static List<VTableComponent> GatherVTableMethodEntries(VTableLayout layo
                              where component.Kind != VTableComponentKind.CompleteDtorPointer &&
                                    component.Kind != VTableComponentKind.RTTI &&
                                    component.Kind != VTableComponentKind.UnusedFunctionPointer &&
+                                   component.Kind != VTableComponentKind.OffsetToTop &&
                                    component.Method != null
                              select component);