Fix getData crashing in offline (#8484)
Fix getData crashing in offline (#8484)

Fixes #8357 

The issue was that `node` property of `FCacheNode` pokes one level deeper: (FCacheNode.m:66)

```
- (id<FNode>)node {
    return self.indexedNode.node;
}
```
firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk