(fix) no error with unkown props if uses $$props

[jasonlyu123]

Currently, unknown props show an error with type ... is not assignable to never when you use $$props and don't have any other props.

For example:

<!-- Component2.svelte -->
<div class={$$props.class}>

<script lang="ts">
import Component2 from './Component2.svelte'
</script>
<Component2 class="abc" />
<!--        ↑↑↑↑↑Type 'string' is not assignable to type 'never'.ts(2322) -->

[dummdidumm]

Good catch, thank you!