fix bogus goal complete with GOAL_NONE

stepmania/src/GameState.cpp

@@ -1867,7 +1867,14 @@ float GameState::GetGoalPercentComplete( PlayerNumber pn )
 		fActual = ssAccum.fGameplaySeconds + ssCurrent.fGameplaySeconds;
 		fGoal = (float)pProfile->m_iGoalSeconds;
 		break;
+	case GOAL_NONE:
+		return 0;	// never complete
+	default:
+		ASSERT(0);
 	}
+	if( fGoal == 0 )
+		return 0;
+	else
 		return fActual / fGoal;
 }