Update NSPR to 4.12 and NSS to 3.23 on iOS

nspr/pr/src/misc/prtpool.c

 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nspr.h"
 
 /*
  * Thread pools
  *      Thread pools create and manage threads to provide support for
@@ skipping 263 matching lines @@
 
 /*
  * io worker thread function
  */
 static void io_wstart(void *arg)
 {
 PRThreadPool *tp = (PRThreadPool *) arg;
 int pollfd_cnt, pollfds_used;
 int rv;
 PRCList *qp, *nextqp;
-PRPollDesc *pollfds;
-PRJob **polljobs;
+PRPollDesc *pollfds = NULL;
+PRJob **polljobs = NULL;
 int poll_timeout;
 PRIntervalTime now;
 
         /*
          * scan io_jobq
          * construct poll list
          * call PR_Poll
          * for all fds, for which poll returns true, move the job to
          * jobq and wakeup worker thread.
          */
@@ skipping 882 matching lines @@
                 delete_job(jobp);
         }
 
         PR_ASSERT(0 == tpool->jobq.cnt);
         PR_ASSERT(0 == tpool->ioq.cnt);
         PR_ASSERT(0 == tpool->timerq.cnt);
 
         delete_threadpool(tpool);
         return rval;
 }