fix an issue where scrollview wouldn't unclip its cells

Summary:
Issue we were seeing: scrollview would clip its cells when it was resized to 0 height and moved offscreen, but it wouldn't add it back when it was resized and moved back
Why this was happening: scrollview wouldn't rerun its un/clipping logic after the first run unless 1/it has 0x0 frame or 2/it has been scrolled. Neither was happening here.
Fix: run the un/clipping logic when scrollview's frame has been changed since the last clipping.

Reviewed By: javache

Differential Revision: D3436996

fbshipit-source-id: 1a8cfeb72b425fcc80815d30743fa308b9c75ab6

React/Views/RCTScrollView.m

@@ -515,6 +515,7 @@ - (void)updateClippedSubviews
 
   const BOOL shouldClipAgain =
     CGRectIsNull(_lastClippedToRect) ||
+    !CGRectEqualToRect(_lastClippedToRect, bounds) ||
     (scrollsHorizontally && (bounds.size.width < leeway || fabs(_lastClippedToRect.origin.x - bounds.origin.x) >= leeway)) ||
     (scrollsVertically && (bounds.size.height < leeway || fabs(_lastClippedToRect.origin.y - bounds.origin.y) >= leeway));