thread_group_close: release mutex in all branches

Found by Coverity scan - id 92087

Author: grooverdan

sql/threadpool_unix.cc

@@ -979,24 +979,26 @@ static void thread_group_close(thread_group_t *thread_group)
 
  if (pipe(thread_group->shutdown_pipe))
  {
- DBUG_VOID_RETURN;
+ goto end;
  }
 
  /* Wake listener */
  if (io_poll_associate_fd(thread_group->pollfd, 
  thread_group->shutdown_pipe[0], NULL))
  {
- DBUG_VOID_RETURN;
+ goto end;
+ }
+ {
+ char c= 0;
+ if (write(thread_group->shutdown_pipe[1], &c, 1) < 0)
+ goto end;
  }
- char c= 0;
- if (write(thread_group->shutdown_pipe[1], &c, 1) < 0)
- DBUG_VOID_RETURN;
-
  /* Wake all workers. */
  while(wake_thread(thread_group) == 0) 
  { 
  }
 
+end:
  mysql_mutex_unlock(&thread_group->mutex);
 
  DBUG_VOID_RETURN;