smp server: deliver later messages after SUB while a delivery waits (#2006)

* smp server: deliver later messages after SUB while a delivery waits

* smp server: reset delivery thread state only for the subscribed client

src/Simplex/Messaging/Server.hs

@@ -2135,7 +2135,7 @@ client
                       ts <- getSystemSeconds
                       atomically $ whenM (sameClient rc rcv) $
                         readTVar delivered >>= \case
-                          Just _ -> pure () -- if a message was already delivered, should not deliver more
+                          Just _ -> writeTVar st NoSub -- if a message was already delivered, should not deliver more
                           Nothing -> do
                             -- a separate thread is needed because it blocks when client sndQ is full.
                             deliver sndQ' s ts