group-view: do not crash on rejoin
Fixes urbit/lansdcape#1113
++ jn-start
|= [rid=resource =^ship]
^+ jn-core
- ?< (~(has by joining) rid)
+ ?> ?= $@(~ [~ %done])
+ (bind (~(get by joining) rid) |=(request:view progress))
=. joining
(~(put by joining) rid [%.n now.bowl ship %start])
=. jn-core
