[mythtv] Playback start race condition

[Kyle Rose]

I've moved this to -dev since I've actually started to dig into the
code.

Background: I'm having this problem on AMD64 that playback usually
doesn't start when I enter live TV or select a recording: the screen
goes black and then the frontend spins, with the only system calls
being writes to and reads from a pipe.

I compiled with debug information and noted that it is spinning in
PlaybackBox::play; specifically, the following code:

programs/mythfrontend/playbackbox.cpp:1402
    if (tv->Playback(tvrec))
    {
        while (tv->GetState() != kState_None)
        {
            qApp->unlock();
            qApp->processEvents();
            usleep(10000);
            qApp->lock();
        }
    }

Obviously processEvents isn't actually setting whatever tv->GetState()
returns to something other than kState_None.  Tomorrow I'll look into
that more closely to see under which conditions it sets the state, but
(as I've said many times before) if anyone has any insight, please let
me know.

Cheers,
Kyle