fix(VFileInput): emit null after VForm reset()

[kingyyy]

fixes #20101

reproduce example

<template>
  <v-app>
    <v-container>
      <v-form ref="form">
        <v-file-input v-model="files" />
      </v-form>
      <v-btn @click="resetForm">reset form</v-btn>
    </v-container>
  </v-app>
</template>

<script setup>
  import { ref } from 'vue'

  const files = ref()
  const form = ref()

  const resetForm = () => form.value.reset()
</script>