Guard against pres_last=undefined in mod_offline

src/mod_offline.erl

@@ -482,8 +482,8 @@ c2s_self_presence({_Pres, #{resend_offline := false}} = Acc) ->
     Acc;
 c2s_self_presence({#presence{type = available} = NewPres, State} = Acc) ->
     NewPrio = get_priority_from_presence(NewPres),
-    LastPrio = case maps:get(pres_last, State, error) of
-		   error -> -1;
+    LastPrio = case maps:get(pres_last, State, undefined) of
+		   undefined -> -1;
 		   LastPres -> get_priority_from_presence(LastPres)
 	       end,
     if LastPrio < 0 andalso NewPrio >= 0 ->