FIX: XFRX Previewer generated dangling reference.
KB-20180511-02
Version
Before XFRX 18.1.0
Symptoms
Ramdom cx00000005.
Object of XFRX#SESSION or of XFRX#LISTENER didn't release.
Cause
Dandling references in XFXR#PREVIEW and between XFRX#PREVIEW and XFRX#CORE.