RefreshControl on initial render will not beginRefresh when refreshing state is false

Summary:
There's an edge case in the `RefreshControl` which causes it to show as refreshing when the state is set to false. When the component is initialized with `refreshing` set to `true` on initial render but set to `false` before `layoutSubviews` is called, it will call `beginRefresh` and ignore its state. That's because `layoutSubviews` never checks if `_currentRefreshingState` is in fact still `true`, it merely assumes it is.

This is fixed by simply doing a check for `_currentRefreshingState` before entering `beginRefresh` from `layoutSubviews`.
Closes https://github.com/facebook/react-native/pull/7556

Differential Revision: D3300124

fbshipit-source-id: d1dce8612e2c03b1f14284d513803d00af4b5c8a

React/Views/RCTRefreshControl.m

@@ -35,7 +35,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
 
   // If the control is refreshing when mounted we need to call
   // beginRefreshing in layoutSubview or it doesn't work.
-  if (_isInitialRender && _initialRefreshingState) {
+  if (_currentRefreshingState && _isInitialRender && _initialRefreshingState) {
     [self beginRefreshing];
   }
   _isInitialRender = false;