[iOS] Ignore scroll action if contentSize smaller than scroller frame.

* demo: http://dotwe.org/vue/aa1af34e5fc745c0f1520e346904682a

Author: huanglei.hl

ios/sdk/WeexSDK/Sources/Component/WXListComponent.mm

@@ -252,6 +252,13 @@ - (void)_handleFirstScreenTime
 
 - (void)scrollToComponent:(WXComponent *)component withOffset:(CGFloat)offset animated:(BOOL)animated
 {
+    UIScrollView *scrollView = (UIScrollView *)self.view;
+    // http://dotwe.org/vue/aa1af34e5fc745c0f1520e346904682a
+    // ignore scroll action if contentSize smaller than scroller frame
+    if (scrollView.contentSize.height < scrollView.frame.size.height) {
+        return;
+    }
+    
     CGPoint contentOffset = _tableView.contentOffset;
     CGFloat contentOffsetY = 0;
 

ios/sdk/WeexSDK/Sources/Component/WXScrollerComponent.mm

@@ -562,6 +562,15 @@ - (void)removeScrollToListener:(WXComponent *)target
 - (void)scrollToComponent:(WXComponent *)component withOffset:(CGFloat)offset animated:(BOOL)animated
 {
     UIScrollView *scrollView = (UIScrollView *)self.view;
+    // http://dotwe.org/vue/aa1af34e5fc745c0f1520e346904682a
+    // ignore scroll action if contentSize smaller than scroller frame
+    if (_scrollDirection == WXScrollDirectionVertical && scrollView.contentSize.height < scrollView.frame.size.height) {
+        return;
+    }
+    if (_scrollDirection == WXScrollDirectionHorizontal && scrollView.contentSize.width < scrollView.frame.size.width) {
+        return;
+    }
+
 
     CGPoint contentOffset = scrollView.contentOffset;
     CGFloat scaleFactor = self.weexInstance.pixelScaleFactor;