Fix the crash in the watch tab

Summary:
BUG:

{F158264042}

Context: The code entered an infinite loop till it crashed. In the implementation of `- (SKSearchResultNode *)searchForQuery:(NSString *)query fromNode:(id)node withElementsAlreadyAdded:(NSMutableSet<NSString *> *)alreadyAdded`, we recurse through the child. In the case when the view was `CKRootComponent` it created a `SKComponentLayoutWrapper` in the call to `[descriptor childForNode: node atIndex: i];`. This wrapper's descriptor used to return the very same view from which it was created when it's children were asked. So this led to an infinite loop.

Reviewed By: kfirapps

Differential Revision: D15266478

fbshipit-source-id: 8035209746b7cb4b8773e2fcbdd4c0a148191304

iOS/Plugins/FlipperKitLayoutPlugin/FlipperKitLayoutComponentKitSupport/SKComponentLayoutDescriptor.mm

@@ -86,7 +86,7 @@
 
 - (id)childForNode:(SKComponentLayoutWrapper *)node atIndex:(NSUInteger)index {
     if (node.children.size() == 0) {
-      return node.component.viewContext.view;
+      return nil;
     }
     return node.children[index];
 }