Spread props on dynamic components fail if no initial value

[Rich-Harris]

Bit of an edge case here...

If you have a <svelte:component> whose this doesn't have a value, and it has spread properties, then any updates will fail because the initial spread 'levels' have not been set. REPL

<button on:click="updateProps()">click me</button>
<svelte:component this={undefined} {...props}/>

{#if error}
  <pre>{error.stack}</pre>
{/if}

<script>
  export default {
    data() {
      return {
        props: {}
      };
    },
    
    methods: {
      updateProps() {
        try {
          this.set({ props: {} });
        } catch (error) {
          this.set({ error });
        }
      }
    }
  };
</script>

Interestingly, the this.set({ error }) in that example also fails, because always Svelte tries to recalculate spread levels, even if nothing has changed. Should also get fixed.