SoundEffect decoding error

I've tested with WAV and MPGA files loaded from disk, and SoundEffect is unable to play these. The error message I get is the following:

QSoundEffect(qaudio): Error decoding source qrc:/Users/nils/Documents/file_example_WAV_5MG.wav 

Steps to reproduce:

1. Have a sound file on disk, somewhere accessible by your application
2. Open up a QML project with a SoundEffect item
3. Set the source URL to your file on disk
4. Call .play() on the SoundEffect

I suspect it's related to how we resolve URLs under the hood. The emitted URL seems to include "qrc" seeming to indicate that we're looking into some embedded Qt resources, which we are not.

Another improvement here is if we can get a more specific error "file not found" whenever we can tell this file does not exist.