Fix compilation for bindings only without scripting internal host defined

Source/Engine/Engine/NativeInterop.cs

@@ -425,6 +425,8 @@ namespace FlaxEngine.Interop
                 var fieldOffsetPtr = (IntPtr*)field.FieldHandle.Value; // Pointer to MonoClassField
                 fieldOffsetPtr += 3; // Skip three pointers (type, name, parent_and_flags)
                 return *(int*)fieldOffsetPtr - IntPtr.Size * 2; // Load the value of a pointer (4 bytes, int32), then subtracting 16 bytes from it (2 pointers for vtable and threadsync)
+#else
+                throw new NotImplementedException();
 #endif
             }