renderer-mesh: fixed bug in getBoundingBox()
renderer-mesh: fixed bug in getBoundingBox()

It might be the case that the renderObject is not yet created and also
that the renderObject is present, but not the mesh itself.

Added some checks.

Fiware/webui.Xml3d.js,ariyapour/xml3d.js,ariyapour/xml3d.js,CCLDESTY/xml3d.js,CCLDESTY/xml3d.js,xml3d/xml3d.js,xml3d/xml3d.js,Fiware/webui.Xml3d.js