增加list view是否存在的判断 review by 草莓

@@ -44,7 +44,7 @@ export default class Brand extends Component {
 
     componentWillReceiveProps(nextProps) {
         if (this.props.selectedChannelId != nextProps.selectedChannelId) {
-            this.listView.scrollTo({x: 0, y: 0, animated: false});
+            this.listView && this.listView.scrollTo({x: 0, y: 0, animated: false});
         }
     }
 
@@ -57,7 +57,7 @@ export default class Brand extends Component {
                this.props.setInitialListSize && this.props.setInitialListSize(item.count);
                this.props.setBrandData && this.props.setBrandData(this.sectionDataKey, this.props.selectedChannelId);
            } else {
-               this.listView.scrollTo({x: 0, y: item.y, animated: false});
+               this.listView && this.listView.scrollTo({x: 0, y: item.y, animated: false});
            }
         }
     }
@@ -68,7 +68,7 @@ export default class Brand extends Component {
             this.sectionDataKey[sectionID].y = y;
             this.props.setBrandData && this.props.setBrandData(this.sectionDataKey, this.props.selectedChannelId);
             if (this.needScrollSection == sectionID) {
-               this.listView.scrollTo({x: 0, y, animated: false});
+               this.listView && this.listView.scrollTo({x: 0, y, animated: false});
             }
         }
     }