Update the flush stat before freeing a dirty index node

This is the fix to the memory access after free.

Change-Id: Ib9ab4e288017f4ebdc1a6f236d88974aaf46fe10
Reviewed-on: http://review.couchbase.org/70456
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>

Author: chiyoung

src/bnodecache.cc

@@ -889,19 +889,18 @@ fdb_status BnodeCacheMgr::flushDirtyIndexNodes(FileBnodeCache* fcache,
             // Move to the shard clean node list
             list_push_back(&fcache->shards[shard_num]->cleanNodes,
                            &dirty_bnode->list_elem);
-
+            flushed += dirty_bnode->getNodeSize();
         } else {
             // Not synced, just discarded
             fcache->numItems--;
             fcache->numItemsWritten--;
             // Decrement memory usage
             bnodeCacheCurrentUsage.fetch_sub(dirty_bnode->getMemConsumption());
+            flushed += dirty_bnode->getNodeSize();
             // Free the dirty node as it can be simply discarded
             delete dirty_bnode;
         }
 
-        flushed += dirty_bnode->getNodeSize();
-
         spin_unlock(&fcache->shards[shard_num]->lock);
 
         if (count == dirty_nodes.size()) {