fix(useFileDialog): not assign capture to input if value is nullable

[aizigao]

Description

should not assign capture to input element if value was nullable, this is what happend

codes

<script setup lang="ts">
import { useFileDialog } from '.'

const { files, open, reset } = useFileDialog()
</script>

<template>
  <button type="button" @click="open()">
    Choose files
  </button>
  <button type="button" :disabled="!files" @click="reset()">
    Reset
  </button>
  <template v-if="files">
    <p>You have selected: <b>{{ files.length }} files</b></p>
    <li v-for="file of files" :key="file.name">
      {{ file.name }}
    </li>
  </template>
</template>

before:

normal.video.mp4

after fixed:

normal.video_new.mp4

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• 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.

[webfansplz]

Duplicated of #2080 .

[antfu]

Thanks. Fixed by #2080