Fixes animated gifs incorrectly looping (#25612)

Summary:
[After migrate to new GIF implementation](#24822), we need to do some cleanup, before, we already unify the gif loop count between iOS and Android, more details please see #21999, so let's unify it again.

## Changelog

[iOS] [Fixed] - Fixes animated gifs incorrectly looping
Pull Request resolved: #25612

Test Plan:
example gif should repeat playback twice.
```
        <Image
          style={styles.gif}
          source={{uri: "https://user-images.githubusercontent.com/475235/47662061-77011f00-db57-11e8-904f-a1824912ace9.gif"}}
        />
```

Reviewed By: sammy-SC

Differential Revision: D16280067

Pulled By: osdnk

fbshipit-source-id: 2351499855f1e0e97c358fa0b3544dd2cc0cf703

Author: zhongwuzw

Libraries/Image/RCTAnimatedImage.m

@@ -87,6 +87,10 @@ - (NSUInteger)imageLoopCountWithSource:(CGImageSourceRef)source
     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++;
+      }
     }
   }
   return loopCount;