apr_pools: follow up to r1883750 and r1883800.

After r1883800, the mutex of a pool in APR_POOL_DEBUG can't be NULL, so
remove useless NULL checks around locking.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1883801 13f79535-47bb-0310-9956-ffa450edef68
1 file changed