Hello, I just run in to this problem too, so I'm resurrecting this thread in case anyone else ever runs into the problem
You need to add the line:
if (index == -1) return false;
at the top of the setPosition function of the class org.newdawn.slick.openal.Audio
ending up with:
public boolean setPosition(float position) {
if (index == -1) return false;
position = position % length;
AL10.alSourcef(store.getSource(index), AL11.AL_SEC_OFFSET, position);
if (AL10.alGetError() != 0) {
return false;
}
return true;
}
For some reason the "index" property isn't checked, even in the latest release of Slick2d (I'll comment on their forums asking for a bug fix)