Fix return type of FetchEvent.preloadResponse

Author: armanbilge

api-reports/2_12.txt

@@ -984,7 +984,7 @@ experimental/serviceworkers/ExtendableMessageEventInit[JT] var scoped: js.UndefO
 experimental/serviceworkers/ExtendableMessageEventInit[JT] var source: js.UndefOr[Client | ServiceWorker | MessagePort]
 experimental/serviceworkers/FetchEvent[SC] def clientId: String
 experimental/serviceworkers/FetchEvent[SC] def isReload: Boolean
-experimental/serviceworkers/FetchEvent[SC] def preloadResponse: js.Promise[Response]
+experimental/serviceworkers/FetchEvent[SC] def preloadResponse: js.Promise[js.UndefOr[Response]]
 experimental/serviceworkers/FetchEvent[SC] def replacesClientId: String
 experimental/serviceworkers/FetchEvent[SC] def request: Request
 experimental/serviceworkers/FetchEvent[SC] def respondWith(promisedResponse: Response | js.Promise[Response]): Unit

api-reports/2_13.txt

@@ -984,7 +984,7 @@ experimental/serviceworkers/ExtendableMessageEventInit[JT] var scoped: js.UndefO
 experimental/serviceworkers/ExtendableMessageEventInit[JT] var source: js.UndefOr[Client | ServiceWorker | MessagePort]
 experimental/serviceworkers/FetchEvent[SC] def clientId: String
 experimental/serviceworkers/FetchEvent[SC] def isReload: Boolean
-experimental/serviceworkers/FetchEvent[SC] def preloadResponse: js.Promise[Response]
+experimental/serviceworkers/FetchEvent[SC] def preloadResponse: js.Promise[js.UndefOr[Response]]
 experimental/serviceworkers/FetchEvent[SC] def replacesClientId: String
 experimental/serviceworkers/FetchEvent[SC] def request: Request
 experimental/serviceworkers/FetchEvent[SC] def respondWith(promisedResponse: Response | js.Promise[Response]): Unit

src/main/scala/org/scalajs/dom/experimental/serviceworkers/ServiceWorkers.scala

@@ -111,7 +111,7 @@ class FetchEvent(typeArg: String, init: js.UndefOr[FetchEventInit])
  */
  def request: Request = js.native
 
- def preloadResponse: js.Promise[Response] = js.native
+ def preloadResponse: js.Promise[js.UndefOr[Response]] = js.native
 
  def clientId: String = js.native