add check for if the target has the property when setting

Author: devsnek

lib/internal/bootstrap/loaders.js

@@ -292,7 +292,11 @@
             if (typeof value === 'function')
               value = methodUnwrapMap.get(value) || value;
             if (ReflectSet(target, prop, value, receiver)) {
-              update(prop, ReflectGet(target, prop, receiver));
+              if (ObjectHasOwnProperty.call(target, prop)) {
+                update(prop, ReflectGet(target, prop, receiver));
+              } else {
+                update(prop, undefined);
+              }
               return true;
             }
             return false;