Fix possible free of uninitialized value in walk_rtree

In rtree_hier_realms, if the first rtree_hier_tweens call failed, the
cleanup handler would free stweens which had not been initialized.
Initialize ctweens and stweens to NULL in the variable declarations to
make the cleanup handler safe.

ticket: 6379
tags: pullup
target_version: 1.7

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@21924 dc483132-0cff-0310-8789-dd5450dbe970

src/lib/krb5/krb/walk_rtree.c

@@ -365,7 +365,7 @@ rtree_hier_realms(
 {
     krb5_error_code retval;
     struct hstate c, s;
-    krb5_data *ctweens, *stweens, *twp, *r, *rp;
+    krb5_data *ctweens = NULL, *stweens = NULL, *twp, *r, *rp;
     size_t nctween, nstween;
 
     *realms = NULL;