fix setting upper/lowerAlphaLimit in Viewer configuration

[TrevorDev]

#6016

This is another way to test this without config.json which i used to test this

        <babylon extends="minimal">
            <model url="https://playground.babylonjs.com/scenes/BoomBox.glb">
                <scaling x="10" y="10" z="10"></scaling>
            </model>
            <camera upper-beta-limit="2.5" lower-beta-limit="1.0" upper-alpha-limit="2.5" lower-alpha-limit="1.0">
                <behaviors>
                    <auto-rotate type="0"></auto-rotate>
                </behaviors>
            </camera>
        </babylon>