afp: fix warning where we tried to NULL data to the output stream
afp: fix warning where we tried to NULL data to the output stream

xkahn/gvfs-cmis,philipl/gvfs,xkahn/gvfs-cmis,gicmo/gvfs,cpatulea/gvfs,xkahn/gvfs-cmis,halfline/gvfs,xkahn/gvfs-cmis,gicmo/gvfs,halfline/gvfs,halfline/gvfs,gicmo/gvfs,gicmo/gvfs,philipl/gvfs,cpatulea/gvfs,philipl/gvfs