Do not store mucsub wrapped messages with no-store hint in offline storage

We already don't store those messages in mam and we don't store messages
that aren't wrapped with that hint in offline, so it make sense to extend
it also to mucsub messages.

src/mod_offline.erl

@@ -405,6 +405,12 @@ need_to_store(_LServer, #message{type = error}) -> false;
 need_to_store(LServer, #message{type = Type} = Packet) ->
     case xmpp:has_subtag(Packet, #offline{}) of
 	false ->
+	    case misc:unwrap_mucsub_message(Packet) of
+		#message{type = groupchat} = Msg ->
+		    need_to_store(LServer, Msg#message{type = chat});
+		#message{} = Msg ->
+		    need_to_store(LServer, Msg);
+		_ ->
 		    case check_store_hint(Packet) of
 			store ->
 			    true;
@@ -431,6 +437,7 @@ need_to_store(LServer, #message{type = Type} = Packet) ->
 				{_, unless_chat_state} ->
 				    not misc:is_standalone_chat_state(Packet)
 			    end
+		    end
 	    end;
 	true ->
 	    false