mainloop: Don't care about the mainloop state variable when waking up the mainloop.

mainloop: Don't care about the mainloop state variable when waking up the mainloop.

If the mainloop is just about to enter polling, but m->state
is not POLLING yet when some other thread calls
pa_mainloop_wakeup(), the mainloop will not be woken up.
It's safe to write to the wakeup pipe at any time, so let's
just remove the check.