Fix caching paging during read.

pkg/analysis_server/lib/src/index/page_node_manager.dart

Index: pkg/analysis_server/lib/src/index/page_node_manager.dart
diff --git a/pkg/analysis_server/lib/src/index/page_node_manager.dart b/pkg/analysis_server/lib/src/index/page_node_manager.dart
index 76fdf3e3621f07819ffdaa29ef816a46e6d2cf63..e03374ab1e1c1551dcb14820df74e550e5b1b17a 100644
--- a/pkg/analysis_server/lib/src/index/page_node_manager.dart
+++ b/pkg/analysis_server/lib/src/index/page_node_manager.dart
@@ -7,10 +7,9 @@ library index.page_node_manager;
 import 'dart:collection';
 import 'dart:typed_data';
 
+import 'package:analysis_server/src/index/b_plus_tree.dart';
 import 'package:analysis_server/src/index/lru_cache.dart';
 
-import 'b_plus_tree.dart';
-
 
 /**
  * A [NodeManager] that caches a specified number of index and leaf nodes.
@@ -59,19 +58,21 @@ class CachingNodeManager<K, V, N> implements NodeManager<K, V, N> {
   @override
   IndexNodeData<K, N> readIndex(N id) {
     IndexNodeData<K, N> data = _indexCache.get(id);
-    if (data != null) {
-      return data;
+    if (data == null) {
+      data = _delegate.readIndex(id);
+      _indexCache.put(id, data);
     }
-    return _delegate.readIndex(id);
+    return data;
   }
 
   @override
   LeafNodeData<K, V> readLeaf(N id) {
     LeafNodeData<K, V> data = _leafCache.get(id);
-    if (data != null) {
-      return data;
+    if (data == null) {
+      data = _delegate.readLeaf(id);
+      _leafCache.put(id, data);
     }
-    return _delegate.readLeaf(id);
+    return data;
   }
 
   @override