alphablending: Fix warning while unreferencing NULL caps
alphablending: Fix warning while unreferencing NULL caps

Change-Id: I8587722afa93480c8867e234613079c632e0eedd

TribeMedia/kms-elements,shelsonjava/kms-elements,shelsonjava/kms-elements,TribeMedia/kms-elements,shelsonjava/kms-elements,TribeMedia/kms-elements