kmswebrtcendpoint: free certificate_pem_file without checking not NULL
kmswebrtcendpoint: free certificate_pem_file without checking not NULL

Change-Id: I6a34055c131f6aaf9fae7a152fdde1cfcee57e5e

KurentoLegacy/gst-kurento-plugins,KurentoLegacy/gst-kurento-plugins,KurentoLegacy/gst-kurento-plugins,KurentoLegacy/gst-kurento-plugins