Migrate manga only after "copy" succeeded

In case the manga should not only be copied but actually migrated, the "migration" actions should only be executed in case the copy actions have succeeded.

src/UtilTypes.d.ts

@@ -25,3 +25,7 @@ type OptionalProperty<T, K extends keyof T> = Omit<T, K> & Partial<Pick<T, K>>;
 type PropertiesNever<T> = { [key in keyof T]?: never };
 
 type OmitFirst<T extends any[]> = T extends [any, ...infer R] ? R : never;
+
+type TupleUnion<U extends string, R extends any[] = []> = {
+    [S in U]: Exclude<U, S> extends never ? [...R, S] : TupleUnion<Exclude<U, S>, [...R, S]>;
+}[U];