plugin-common 中未配置 onGroupMemberRequest 时报错

[dragon-fish]

Describe the bug
如果在 plugin-common 的配置项中没有配置 onGroupMemberRequest，bot 收到入群申请时会报错 TypeError: result is not iterable (cannot read property undefined)

To Reproduce

1. 假设简单的注册了插件未作任何配置
   App.plugin(require('koishi-plugin-common'), {})
2. 将 bot 设置为管理员以便接受入群申请消息。
3. 有用户申请入群：see bug

Expected behavior

既不做处理，也不报错

Screenshots

TypeError: result is not iterable (cannot read property undefined)
    at _Session.<anonymous> (C:\QQbot-SILI\node_modules\koishi-plugin-common\lib\index.js:682:24)
        -> (C:\QQbot-SILI\node_modules\koishi-plugin-common\src\handler.ts:114:24)
    at processTicksAndRejections (node:internal/process/task_queues:93:5)
    at async Promise.all (index 1)

Versions

• OS: [e.g. iOS]
• Node Version: [e.g. 10.16.0] 15.4.0
• CoolQ Version: 1.0.0-beta.1
• CQHTTP Version: -
• Koishi Version: 3.7.0
• plugin-common: 4.2.1

Additional context