prevent exception if fucntion not defined in window
prevent exception if fucntion not defined in window

Change-Id: I86750d7f3376d8a46f6db18082c9c1f73f2ff97a

lcamacho/kurento-utils-js,shelsonjava/kurento-utils-js,lcamacho/kurento-utils-js,shelsonjava/kurento-utils-js