Fix track locking via "config tracks" dialog not working properly:

[kdenlive] / effects / sox_vibro.xml

<!DOCTYPE kpartgui>
<effect tag="sox" id="sox_vibro" type="audio">
        <name>Sox Vibro</name>
        <description>Sox vibro audio effect</description>
        <author>http://sox.sourceforge.net</author>
        <parameter type="constant" name="speed" max="30" min="1" default="15">
                <name>Speed</name>
        </parameter>
</effect>