tree: crash when root is to be replaced.

* tree.c (tr_insert): When the inserted key matches the root
node, then there is nothing in ti->path and ti->depth is zero.
We are accessing ti->path[-1] to get a root node.  We must
test for zero depth and install the new node as the tree root
in that case.

1 files changed, 9 insertions, 4 deletions

diff --git a/tree.c b/tree.c
index 45132648..b7e528eb 100644
--- a/tree.c
+++ b/tree.c
@@ -265,11 +265,16 @@ static void tr_insert(struct tree *tr, struct tree_iter *ti,
     val parent = ti->path[ti->depth - 1];
     node->tn.left = subtree->tn.left;
     node->tn.right = subtree->tn.right;
+    if (ti->depth > 0) {
+      val parent = ti->path[ti->depth - 1];
 
-    if (parent->tn.left == subtree)
-      parent->tn.left = node;
-    else
-      parent->tn.right = node;
+      if (parent->tn.left == subtree)
+        parent->tn.left = node;
+      else
+        parent->tn.right = node;
+    } else {
+      tr->root = node;
+    }
   } else {
     if (subtree->tn.right) {
       ti->path[ti->depth++] = subtree;