CustomError doesn't work when using Worker

[nguyenyou]

Related issue: pinojs/thread-stream#29

In short, the custom error PdfEngineError after sending back to the main thread will become Error and we lose all the custom fields.

export class PdfEngineError extends Error {
    /**
     * Error code
     */
    code?: number;
    /**
     *
     * @param message - error message
     * @param code - error code
     */
    constructor(message: string, code?: number);
}

As a workaround, I think I will put the code as part of the message.