- update floor/ceiling for inventory items after traveling

Inventory items had dangling floor and ceiling sector pointers after transition to a new level
This could cause random issues with serialization

https://forum.zdoom.org/viewtopic.php?t=67494

src/g_level.cpp

@@ -1550,6 +1550,7 @@ int FLevelLocals::FinishTravel ()
 		{
 			inv->ChangeStatNum (STAT_INVENTORY);
 			inv->LinkToWorld (nullptr);
+			P_FindFloorCeiling(inv, FFCF_ONLYSPAWNPOS);
 
 			IFVIRTUALPTRNAME(inv, NAME_Inventory, Travelled)
 			{