Android asset manager needs consistent error handling

```
Sound: currently returns an error sound, but this sound should probably log and 
error on play
Image: currently returns null (bad), needs to return an error image like Java 
does
Text: currently doesn't handle null (bad), should call into error handler 
instead

```

Original issue reported on code.google.com by `mmast...@gmail.com` on 4 Jul 2011 at 4:03
