【报Bug】WXSDKInstance.getInstanceViewPortWidth() 空指针问题

bugly上抓到的关键日志：
java.lang.NullPointerException
Attempt to invoke virtual method 'int com.taobao.weex.WXSDKInstance.getInstanceViewPortWidth()' on a null object reference
com.taobao.weex.ui.component.list.BasicListComponent.getScrollEvent(BasicListComponent.java:1396)
com.taobao.weex.ui.component.list.BasicListComponent.fireScrollEvent(BasicListComponent.java:1379)
com.taobao.weex.ui.component.list.BasicListComponent.access$600(BasicListComponent.java:94)
com.taobao.weex.ui.component.list.BasicListComponent$7.onScrolled(BasicListComponent.java:1371)