Don't show subscribed but non-existent folders.
Don't show subscribed but non-existent folders.

The RFCs are clear that it's OK to have non-existent folders in the
subscribed list. Don't treat them as if they were real folders -- just
use their existence in the LSUB response to set the SUBSCRIBED flag if they
were already returned by the LIST response.

matzipan/evolution-data-server,gcampax/evolution-data-server,gcampax/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,Distrotech/evolution-data-server,gcampax/evolution-data-server,tintou/evolution-data-server,tintou/evolution-data-server,Distrotech/evolution-data-server,tintou/evolution-data-server,gcampax/evolution-data-server,Distrotech/evolution-data-server,Distrotech/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,Distrotech/evolution-data-server,tintou/evolution-data-server