fix invalid memory address or nil pointer error

pkg/compute/models/storagecaches.go

@@ -378,7 +378,7 @@ func (self *SStoragecache) StartImageUncacheTask(ctx context.Context, userCred m
 func (self *SStoragecache) GetIStorageCache() (cloudprovider.ICloudStoragecache, error) {
 	storages := self.getValidStorages()
 	if len(storages) == 0 {
-		msg := "no storages for this storagecache???"
+		msg := fmt.Sprintf("no storages for this storagecache %s(%s)???", self.Name, self.Id)
 		log.Errorf(msg)
 		return nil, fmt.Errorf(msg)
 	}

pkg/util/zstack/storagecache.go

@@ -123,6 +123,7 @@ func (self *SStoragecache) uploadImage(ctx context.Context, userCred mcclient.To
 	if err != nil {
 		return "", err
 	}
+	img.storageCache = self
 	err = cloudprovider.WaitStatus(img, api.CACHED_IMAGE_STATUS_READY, time.Second*5, time.Minute*10) //windows镜像转换比较慢，等待时间稍微设长一些
 	if err != nil {
 		log.Errorf("waitting for image %s(%s) status ready timeout", img.Name, img.UUID)