chore: Get rid of redundant code

Author: bigyifeng

packages/vue-virtual-scroller/src/components/RecycleScroller.vue

@@ -378,7 +378,8 @@ export default {
     handleScroll (event) {
       if (!this.$_scrollDirty) {
         this.$_scrollDirty = true
-        this.$emit('scroll-start', this.getScroll());
+        const scroll = this.getScroll()
+        this.$emit('scroll-start',scroll);
         if (this.$_updateTimeout) return
 
         const requestUpdate = () => requestAnimationFrame(() => {
@@ -390,7 +391,7 @@ export default {
           if (!continuous) {
             clearTimeout(this.$_refreshTimeout)
             this.$_refreshTimeout = setTimeout(this.handleScroll, this.updateInterval + 100)
-            this.$emit('scroll-end', this.getScroll());
+            this.$emit('scroll-end', scroll);
           }
         })