fix: additional check for component on destroy (svelte4) (#11489)

fixes #10454

.changeset/many-trainers-pretend.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: check if svelte component exists on custom element destroy

packages/svelte/src/runtime/internal/Component.js

@@ -335,7 +335,7 @@ if (typeof HTMLElement === 'function') {
 			this.$$cn = false;
 			// In a microtask, because this could be a move within the DOM
 			Promise.resolve().then(() => {
-				if (!this.$$cn) {
+				if (!this.$$cn && this.$$c) {
 					this.$$c.$destroy();
 					this.$$c = undefined;
 				}