Make delete-role idempotent

os2.rkt

@@ -193,6 +193,8 @@
 					      hs))]))
 
 (define (do-unsubscribe pid eid reason state)
+  (cond
+   [(hash-has-key? (vm-endpoints state) eid)
     (define endpoint-to-remove (hash-ref (vm-endpoints state) eid))
     (define removed-topic (endpoint-topic endpoint-to-remove))
     (define old-process (hash-ref (vm-processes state) pid))
@@ -216,7 +218,8 @@
 		   (handlers-absence (endpoint-handlers e))
 		   matching-eid
 		   outbound-flow
-		 reason))))
+		   reason)))]
+   [else state]))
 
 (define (route-and-deliver message-topic body state)
   (define pids-and-endpoints