fix(useIDBKeyval): incorrect value init set

[sun0day]

Description

useIDBKeyval has some problems in L58-L59. This PR purpose is to solve these problems below.

• Only undefined and null rawInit should be ignored to set
• Since set is an async method, it is unsafe without await(L65-L67 can't catch error when set error).

vueuse/packages/integrations/useIDBKeyval/index.ts

Lines 54 to 70 in 0a49ea4

	async function read() {
	try {
	const rawValue = await get<T>(key)
	if (rawValue === undefined) {
	if (rawInit)
	set(key, rawInit)
	}
	else {
	data.value = rawValue
	}
	}
	catch (e) {
	onError(e)
	}
	}
	read()

Additional context

Unit test covered.

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[sun0day]

@sxzz @antfu cc