only call without_reactive_context when the controller exists

packages/svelte/src/internal/client/reactivity/effects.js

@@ -407,9 +407,13 @@ export function destroy_effect_children(signal, remove_dom = false) {
 	signal.first = signal.last = null;
 
 	while (effect !== null) {
-		without_reactive_context(() => {
+		const controller = effect.ac;
-			/** @type {Effect} */ (effect).ac?.abort(STALE_REACTION);
+
-		});
+		if (controller !== null) {
+			without_reactive_context(() => {
+				controller.abort(STALE_REACTION);
+			});
+		}
 
 		var next = effect.next;
 

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

@@ -282,6 +282,7 @@ export function update_reaction(reaction) {
 		without_reactive_context(() => {
 			/** @type {AbortController} */ (reaction.ac).abort(STALE_REACTION);
 		});
+
 		reaction.ac = null;
 	}