Fix a small memory leak.

Found by someone reading the code, rather than because we saw a crash. This is
only a small leak, and you'd have to be dumping threads (because of an ANR) or
creating a new thread to provoke it.

(cherry picked from commit 6d1a1dfd0ef006e19067b6ffd927160d0c6d9647)

Change-Id: Id857efca8d34b20d1acaa452c3fe5d2975e2572b