QNetworkAccessCache: Another fix to the linked list insertion

When inserting between two nodes the "previous" node's "newer" was
forgotten and not updated. So every node's "newer" would point to the
"newest" node.

Change-Id: I5b0df8812be5f7f62b3ae363e4c78f582e0e5c43
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/network/access/qnetworkaccesscache.cpp

@@ -173,6 +173,8 @@ void QNetworkAccessCache::linkEntry(const QByteArray &key)
                 current = current->older;
             }
             node->older = current->older;
+            if (node->older)
+                node->older->newer = node;
             node->newer = current;
             current->older = node;
             if (node->older == nullptr) {