Update RCTScrollView.m

Summary:
fix problem of function scrollToEnd: There are some strange thing happened when contentSize.height(width)  is smaller than bounds.size.height(width).  In fact, there is no need to scroll in this case.

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Closes #13180

Differential Revision: D4928778

Pulled By: javache

fbshipit-source-id: 8b74833593ee317df726a4035ec71bbc77d13afe

React/Views/RCTScrollView.m

@@ -525,9 +525,11 @@ - (void)scrollToEnd:(BOOL)animated
   BOOL isHorizontal = [self isHorizontal:_scrollView];
   CGPoint offset;
   if (isHorizontal) {
-    offset = CGPointMake(_scrollView.contentSize.width - _scrollView.bounds.size.width, 0);
+    CGFloat offsetX = _scrollView.contentSize.width - _scrollView.bounds.size.width;
+    offset = CGPointMake(MAX(offsetX, 0), 0);
   } else {
-    offset = CGPointMake(0, _scrollView.contentSize.height - _scrollView.bounds.size.height);
+    CGFloat offsetY = _scrollView.contentSize.height - _scrollView.bounds.size.height;
+    offset = CGPointMake(0, MAX(offsetY, 0));
   }
   if (!CGPointEqualToPoint(_scrollView.contentOffset, offset)) {
     // Ensure at least one scroll event will fire