Remove redundant queue switch from RCTLocalAssetImageLoader

Summary:
Switching queues in `RCTLocalAssetImageLoader` is unnecessary. We dispatch to main queue before assigning the image to `UIImageView`.

Changelog: Remove redundant queue switch from RCTLocalAssetImageLoader

Reviewed By: PeteTheHeat

Differential Revision: D20347223

fbshipit-source-id: ff6215838f0462356d4a516e6ec31c82a742881a

Libraries/Image/RCTLocalAssetImageLoader.mm

@@ -49,28 +49,19 @@ - (RCTImageLoaderCancellationBlock)loadImageForURL:(NSURL *)imageURL
                                  partialLoadHandler:(RCTImageLoaderPartialLoadBlock)partialLoadHandler
                                   completionHandler:(RCTImageLoaderCompletionBlock)completionHandler
 {
-  __block auto cancelled = std::make_shared<std::atomic<bool>>(false);
-  RCTExecuteOnMainQueue(^{
-    if (cancelled->load()) {
-      return;
+  UIImage *image = RCTImageFromLocalAssetURL(imageURL);
+  if (image) {
+    if (progressHandler) {
+      progressHandler(1, 1);
     }
-
-    UIImage *image = RCTImageFromLocalAssetURL(imageURL);
-    if (image) {
-      if (progressHandler) {
-        progressHandler(1, 1);
-      }
-      completionHandler(nil, image);
-    } else {
-      NSString *message = [NSString stringWithFormat:@"Could not find image %@", imageURL];
-      RCTLogWarn(@"%@", message);
-      completionHandler(RCTErrorWithMessage(message), nil);
-    }
-  });
-
-  return ^{
-    cancelled->store(true);
-  };
+    completionHandler(nil, image);
+  } else {
+    NSString *message = [NSString stringWithFormat:@"Could not find image %@", imageURL];
+    RCTLogWarn(@"%@", message);
+    completionHandler(RCTErrorWithMessage(message), nil);
+  }
+
+  return nil;
 }
 
 @end