Move lock acquire/release functions to safer locations in task deque cleanup code

[hbae]

Summary

The original locations can be reached without initializing the lock variable (td_deque_lock), so it is potentially unsafe.
It is guaranteed that the lock is initialized if the deque (td_deque) is not NULL, and lock functions can be safely called.

[tlwilmar]

LGTM

openmp/trunk/runtime/src/kmp_tasking.cpp

static void __kmp_realloc_task_deque(kmp_info_t *thread,
   thread_data->td.td_deque = new_deque;
   thread_data->td.td_deque_size = new_size;
 }
 
 // __kmp_free_task_deque:
 // Deallocates a task deque for a particular thread. Happens at library
 // deallocation so don't need to reset all thread data fields.
 static void __kmp_free_task_deque(kmp_thread_data_t *thread_data) {
-  __kmp_acquire_bootstrap_lock(&thread_data->td.td_deque_lock);
-
   if (thread_data->td.td_deque != NULL) {
+    __kmp_acquire_bootstrap_lock(&thread_data->td.td_deque_lock);
     TCW_4(thread_data->td.td_deque_ntasks, 0);
     __kmp_free(thread_data->td.td_deque);
     thread_data->td.td_deque = NULL;
-  }
     __kmp_release_bootstrap_lock(&thread_data->td.td_deque_lock);
+  }
 
 #ifdef BUILD_TIED_TASK_STACK
   // GEH: Figure out what to do here for td_susp_tied_tasks
   if (thread_data->td.td_susp_tied_tasks.ts_entries != TASK_STACK_EMPTY) {
     __kmp_free_task_stack(__kmp_thread_from_gtid(gtid), thread_data);
   }
 #endif // BUILD_TIED_TASK_STACK
 }