fix crash on reload during animation

Summary:
closes #11719

**Test plan (required)**

Cmd+r during native animation in uiexplorer
Closes https://github.com/facebook/react-native/pull/11720

Differential Revision: D4386449

fbshipit-source-id: a7b5ea2c77de260e8b95b5983438f9cef4d1d752

Libraries/NativeAnimation/RCTNativeAnimatedNodesManager.m

@@ -321,7 +321,14 @@
 
 - (void)stopAnimationLoopIfNeeded
 {
-  if (_displayLink && _activeAnimations.count == 0) {
+  if (_activeAnimations.count == 0) {
+    [self stopAnimationLoop];
+  }
+}
+
+- (void)stopAnimationLoop
+{
+  if (_displayLink) {
     [_displayLink invalidate];
     _displayLink = nil;
   }