Fix XSL error when multiple hierarchyLevel are set
Applied commit from ticket http://trac.osgeo.org/geonetwork/ticket/406 to MCP
https://github.com/geonetwork/core-geonetwork/commit/b93fdfd4b0e3f2a754e026b6fa5ad86a3349dd0e#diff-c1cd68efff5e65dbafc49a95adb0b721L449