rb_tree: fix possible access-after-free-error in trbt_traversearray32_node

rb_tree: fix possible access-after-free-error in trbt_traversearray32_node

When the traverse callback frees the current node, the traverse of the
rbtree can fail (the next node->right fails since node is not there any more...).
This is fixed by introducing variables to store the right (and left)
pointers before the callback is called.
(cherry picked from commit 8b0caaeed154d26c67a73659d3bbbdd63b21be11)