Fix spurious 'Missing event data' error for triggerEnd objectives with no coordinates

QuestieQuestPrivates.lua: event handler now returns nil silently when
Coordinates is nil, instead of logging a visible error. Nil coordinates
are valid for server-tracked objectives (complete N quests in zone) that
have no map pin.

Modules/Quest/QuestieQuestPrivates.lua

@@ -170,8 +170,8 @@ end
 event = function(eventId, objective)
     local spawns = objective.Coordinates
     if (not spawns) then
-        Questie:Error("Missing event data for Objective:", objective.Description, "id:", eventId)
-        spawns = {}
+        Questie:Debug(Questie.DEBUG_DEVELOP, "No coordinates for event objective:", objective.Description, "id:", eventId)
+        return nil
     end
 
     ---@type SpawnListEvent