Music/Speech Pin detection problem

The micro:bit music module doesn't appear to detect that the speaker is connected to pins 0 and 1 (as it should) causing it to be silent or very quiet. However, once speech takes place the pins are correctly configured. I believe there is a detection step in the speech module that doesn't appear to occur for the music module.

To re-create, plug in a speaker to pins 0 and 1 and, try the following REPL interaction:

```
>>> import music
>>> music.play(music.NYAN) # very very quiet
>>> import speech
>>> speech.say("Hello") # at the correct volume
>>> music.play(music.NYAN) # at the correct volume
```

Music plays at the correct volume if I connect the speaker to pins 0 and GND (as we used to have to do). But part of the point of the new pin code / audio work was that it would correctly detect the use of non-ground pins (so speech would work better) and audio output would be at the correct volume.

I hope this makes sense. Happy to answer questions.