imageoverlay: Not draw a circle if an overlay image is not defined
imageoverlay: Not draw a circle if an overlay image is not defined

Change-Id: I8f5e9ada5bddec95362269cb3a19a94e18cdaccb

KurentoLegacy/gst-kurento-plugins,Kurento/kms-core,ESTOS/kms-core,TribeMedia/kms-core,Kurento/kms-core,shelsonjava/kms-core,ESTOS/kms-core,ESTOS/kms-core,TribeMedia/kms-core,TribeMedia/kms-core,shelsonjava/kms-core,KurentoLegacy/gst-kurento-plugins,KurentoLegacy/gst-kurento-plugins,shelsonjava/kms-core,Kurento/kms-core,Kurento/kms-core,ESTOS/kms-core,TribeMedia/kms-core,KurentoLegacy/gst-kurento-plugins,shelsonjava/kms-core