BFS: Fix vising attribute runs in FileSystemVisitor.

See inline comment. Fixes "vnode refcount > 0" assert failures while
running checkfs after yesterday's commits.

src/add-ons/kernel/file_systems/bfs/FileSystemVisitor.cpp

@@ -163,6 +163,12 @@ FileSystemVisitor::Next()
 		if ((fFlags & VISIT_ATTRIBUTE_DIRECTORIES)
 				&& !inode->Attributes().IsZero()) {
 			fStack.Push(inode->Attributes());
+
+			// We may already be keeping the associated Vnode, so we can't
+			// just call vnode.Keep() here, but rather acquire another reference
+			// to it specifically.
+			Vnode attrNode(fVolume, inode->Attributes());
+			attrNode.Keep();
 		}
 
 		bool visitingCurrentDirectory = inode->BlockRun() == fCurrent;