Fix a leak related to use of function used in a closure (apollographq…

…l/apollo-ios-dev#457)

Sources/Apollo/ApolloStore.swift

@@ -202,8 +202,12 @@ public class ApolloStore {
 
   public class ReadTransaction {
     fileprivate let cache: any NormalizedCache
+
+    fileprivate lazy var loader: DataLoader<CacheKey, Record> = DataLoader { [weak self] batchLoad in
+          guard let self else { return [:] }
+          return try cache.loadRecords(forKeys: batchLoad)
+    }
 
-    fileprivate lazy var loader: DataLoader<CacheKey, Record> = DataLoader(self.cache.loadRecords)
     fileprivate lazy var executor = GraphQLExecutor(
       executionSource: CacheDataExecutionSource(transaction: self)
     )