fix(ImagePreview): should not close when click index (#4764)

src/image-preview/index.less

@@ -7,6 +7,10 @@
   width: 100%;
   height: 100%;
 
+  &__swipe {
+    height: 100%;
+  }
+
   &__image {
     position: absolute;
     top: 0;
@@ -33,8 +37,4 @@
   &__overlay {
     background-color: @image-preview-overlay-background-color;
   }
-
-  .van-swipe {
-    height: 100%;
-  }
 }