BUG/MEDIUM: threads: don't close the thread waker pipe if not init

BUG/MEDIUM: threads: don't close the thread waker pipe if not init

This bugfix concerns the thread deinit but affects the master process.

When the master process falls in wait mode (it fails to reload the
configuration), it launches the deinit_pollers_per_thread and close the
thread waker pipe. It closes rd (-1) and wr (0).

Closing a FD in the master can have several sides effects and the
process will probably quit at some point.

In this case it assigns 0 to the socketpair of a worker during the next
correct reload, and then closes the socketpair once it falls in wait
mode again. The worker assumes that the master died and leaves.