agnosticbin: get a reference of the event
agnosticbin: get a reference of the event

Event reference is lost calling to gst_pad_event_default.

Change-Id: I1d809df0fc90769dc09d5601c95f7c390809f315

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