Fix image loop counter on iOS 14 (#30744)

Summary:
Animated gifs, which do not loop, currently animate twice on iOS 14.
See: https://github.com/facebook/react-native/issues/30147

## Changelog

[iOS] [Fixed] - Animated images without loop no longer animate twice

Pull Request resolved: https://github.com/facebook/react-native/pull/30744

Test Plan:
Run the example app with any animated gif. I attached a gif, which is affected.

![checkmark](https://user-images.githubusercontent.com/54310840/104746529-b2e02900-574f-11eb-9870-0c03c769c990.gif)

Reviewed By: sammy-SC

Differential Revision: D25977626

Pulled By: PeteTheHeat

fbshipit-source-id: 889d4a7bed8f7a7be6a9a427501d0071b7c02b8c

Libraries/Image/RCTAnimatedImage.m

@@ -87,9 +87,12 @@
     NSNumber *gifLoopCount = gifProperties[(__bridge NSString *)kCGImagePropertyGIFLoopCount];
     if (gifLoopCount != nil) {
       loopCount = gifLoopCount.unsignedIntegerValue;
-      // A loop count of 1 means it should repeat twice, 2 means, thrice, etc.
-      if (loopCount != 0) {
-        loopCount++;
+      if (@available(iOS 14, *)) {
+      } else {
+      // A loop count of 1 means it should animate twice, 2 means, thrice, etc.
+        if (loopCount != 0) {
+          loopCount++;
+        }
       }
     }
   }