SFC: `no-unused-keys` without <template> not working

[wolfgangwalther]

Currently you need at least an empty <template> tag in a SFC to make the no-unused-keys rule work.

The following results in DONE No lint errors found!:

<i18n lang="yaml" locale="en">
test: Test
</i18n>

<script>
export default {
  render (createElement) {
    return createElement('div')
  }
}
</script>

While the following correctly throws error: unused 'test' key (@intlify/vue-i18n/no-unused-keys) at [...]:

<i18n lang="yaml" locale="en">
test: Test
</i18n>

<template>
  <div/>
</template>

I expect the first example to throw the same error.