Fix warnings for watchOS

Sources/Extensions/WKInterfaceImage+Kingfisher.swift

@@ -80,8 +80,14 @@ extension KingfisherWrapper where Base: WKInterfaceImage {
             completionHandler: { result in
                 CallbackQueue.mainCurrentOrAsync.execute {
                     guard issuedTaskIdentifier == self.taskIdentifier else {
-                        let error = KingfisherError.imageSettingError(
-                            reason: .notCurrentSourceTask(result: result.value, error: result.error, source: source))
+                        let reason: KingfisherError.ImageSettingErrorReason
+                        do {
+                            let value = try result.get()
+                            reason = .notCurrentSourceTask(result: value, error: nil, source: source)
+                        } catch {
+                            reason = .notCurrentSourceTask(result: nil, error: error, source: source)
+                        }
+                        let error = KingfisherError.imageSettingError(reason: reason)
                         completionHandler?(.failure(error))
                         return
                     }