Fix usage items under player

[ArturKnopik]

Pull Request Prelude

• I have followed [proper The Forgotten Server code styling][code].
• I have read and understood the [contribution guidelines][cont] before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

Fix usage items under player
closes #4001

How to test

1. Put item under player, for example mana potion
2. Use item

---

1. Stay under door
2. try close the door

Code author: @Zbizu

[Zbizu]

correct, original diff (private repo):

diff --git a/src/tile.cpp b/src/tile.cpp
index b748de0c2..5b42a8b8e 100644
--- a/src/tile.cpp
+++ b/src/tile.cpp
@@ -1606,12 +1606,31 @@ bool Tile::isMoveableBlocking() const
 Item* Tile::getUseItem(int32_t index) const
 {
 	const TileItemVector* items = getItemList();
+
+	// no items, get ground
 	if (!items || items->size() == 0) {
 		return ground;
 	}
 
+	// try getting thing by index
 	if (Thing* thing = getThing(index)) {
-		return thing->getItem();
+		Item* thingItem = thing->getItem();
+		if (thingItem) {
+			return thingItem;
+		}
+	}
+
+	// try getting top usable item
+	Item* topDownItem = getTopDownItem();
+	if (topDownItem) {
+		return topDownItem;
+	}
+
+	// try getting door
+	for (auto it = items->rbegin(), end = items->rend(); it != end; ++it) {
+		if ((*it)->getDoor()) {
+			return (*it)->getDoor();
+		}
 	}
 
 	return nullptr;

[Zbizu]

top movable*

[Zbizu]

This needs to stay. It returns top immovable item (eg. field or splash)