chore(Table): add threshold

Author: youluna

src/table/virtual.jsx

@@ -7,6 +7,7 @@ import VirtualBody from './virtual/body';
 import { statics } from './util';
 
 const noop = () => {};
+const THRESHOLD = 10;
 export default function virtual(BaseComponent) {
     class VirtualTable extends React.Component {
         static VirtualBody = VirtualBody;
@@ -143,7 +144,9 @@ export default function virtual(BaseComponent) {
                 return 0;
             }
 
-            return this.start * rowHeight;
+            const start = Math.max(this.start - THRESHOLD, 0);
+
+            return start * rowHeight;
         }
 
         getVisibleRange(ExpectStart) {
@@ -273,7 +276,7 @@ export default function virtual(BaseComponent) {
                 dataSource.forEach((current, index, record) => {
                     if (!current.hidden) {
                         count += 1;
-                        if (count >= start && count < end) {
+                        if (count >= Math.max(start - THRESHOLD, 0) && count < end) {
                             newDataSource.push(current);
                         }
                     }