fix(ImagePreview): missing initial animation (#8274)

src/image-preview/ImagePreview.js

@@ -215,18 +215,16 @@ export default createComponent({
   },
 
   render() {
-    if (!this.shouldRender) {
-      return;
-    }
-
     return (
       <transition name={this.transition} onAfterLeave={this.onClosed}>
+        {this.shouldRender ? (
           <div vShow={this.value} class={[bem(), this.className]}>
             {this.genClose()}
             {this.genImages()}
             {this.genIndex()}
             {this.genCover()}
           </div>
+        ) : null}
       </transition>
     );
   },