fix: more const ref

Author: dudantas

src/items/containers/container.cpp

@@ -386,7 +386,7 @@ uint32_t Container::getContainerHoldingCount() {
 bool Container::isHoldingItem(const std::shared_ptr<Item> &item) {
 	for (ContainerIterator it = iterator(); it.hasNext(); it.advance()) {
 		const auto &compareItem = *it;
-		if (!compareItem) {
+		if (!compareItem || !item) {
 			continue;
 		}
 

src/items/containers/mailbox/mailbox.cpp

@@ -99,7 +99,8 @@ bool Mailbox::sendItem(const std::shared_ptr<Item> &item) const {
 	}
 	if (player && item) {
 		const auto &playerInbox = player->getInbox();
-		if (g_game().internalMoveItem(item->getParent(), playerInbox, INDEX_WHEREEVER, item, item->getItemCount(), nullptr, FLAG_NOLIMIT) == RETURNVALUE_NOERROR) {
+		const auto &itemParent = item->getParent();
+		if (g_game().internalMoveItem(itemParent, playerInbox, INDEX_WHEREEVER, item, item->getItemCount(), nullptr, FLAG_NOLIMIT) == RETURNVALUE_NOERROR) {
 			const auto &newItem = g_game().transformItem(item, item->getID() + 1);
 			if (newItem && newItem->getID() == ITEM_LETTER_STAMPED && !writer.empty()) {
 				newItem->setAttribute(ItemAttribute_t::WRITER, writer);

src/map/house/house.cpp

@@ -849,7 +849,7 @@ void Houses::payHouses(RentPeriod_t rentPeriod) const {
 			if (house->getPayRentWarnings() < 7) {
 				const int32_t daysLeft = 7 - house->getPayRentWarnings();
 
-				std::shared_ptr<Item> letter = Item::CreateItem(ITEM_LETTER_STAMPED);
+				const std::shared_ptr<Item> &letter = Item::CreateItem(ITEM_LETTER_STAMPED);
 				std::string period;
 
 				switch (rentPeriod) {