fix(backend): ensure currentAppRecord is defined when backend handli…

[dO-ob94]

…ng components events emitted from Vue. (fix #1770)

Description

I have noticed that there are some issues caused by the reason that currentAppRecord is not defined (but it is used when some hooks such as COMPONENT_ADDED are called). Typical issues are #1770 and #1711. And there is good case analysis.

I had same issue when I developed a Micro Frontends project which contains both Vue2 and Vue3 app instance. And I found that selectApp function is almost a synchronous function. So I just change the order of code execution in createAppRecord function then errors disappeared.

@yyx990803 吐槽一下，这个二十几k星项目的文档还有很大的提升空间。

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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