route: skip arrow updates while frame is not ready

There seem to be issues with the loading order here lately without
having anything changed in the code. Maybe again related to windows
updates that changed timing behaviour somewhere.

route.lua

@@ -328,6 +328,9 @@ local defcolor = "|cffffcc00"
 local r, g, b
 
 pfQuest.route.arrow:SetScript("OnUpdate", function()
+  -- abort if the frame is not initialized yet
+  if not this.parent then return end
+
   xplayer, yplayer = GetPlayerMapPosition("player")
   wrongmap = xplayer == 0 and yplayer == 0 and true or nil
   target = this.parent.coords and this.parent.coords[1] and this.parent.coords[1][4] and this.parent.coords[1] or nil