Add protect when save task (#466)

Summary:
Bugfix

Add protect when save task

If local cache resource are valid, we don't create a Task .So here are crash.
Pull Request resolved: https://github.com/facebook/flipper/pull/466

Reviewed By: passy

Differential Revision: D15851816

Pulled By: priteshrnandgaonkar

fbshipit-source-id: 753b3c5c9a6ed4c703c934a89e45fa30df99068c

iOS/Plugins/FlipperKitNetworkPlugin/SKIOSNetworkPlugin/FLEXNetworkLib/FLEXNetworkObserver.mm

@@ -847,7 +847,10 @@ static char const *const kFLEXRequestIDKey = "kFLEXRequestIDKey";
 
 + (void)setRequestID:(NSString *)requestID forConnectionOrTask:(id)connectionOrTask
 {
+    if (connectionOrTask) {
         objc_setAssociatedObject(connectionOrTask, kFLEXRequestIDKey, requestID, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
+    }
+    
 }
 
 #pragma mark - Initialization