message: feat(ImagePreview): improve error image style
diff: -webkit-user-drag: none;
  }
  - .van-image__loading {
  + .van-image {
  + &__error {
  + top: 30%;
  + height: 40%;
  + }
  +
  + &__error-icon {
  + font-size: 36px;
  + }
  +
  + &__loading {
  background-color: transparent;
  }
  }
  + }
  &__index {
  position: absolute;
  