🐛 Use 'Spell' instead of 'RSpell' for clearing used inventory scrolls

Readied spell can be swapped to something else in between the cast and the hit frame, resulting in incorrect removal.

This is how currently belt scrolls are checked so we are now using a consistent strategy.

Source/inv.cpp

@@ -1911,7 +1911,7 @@ void RemoveScroll(Player &player)
 	for (int i = 0; i < player._pNumInv; i++) {
 		if (!player.InvList[i].isEmpty()
 		    && (player.InvList[i]._iMiscId == IMISC_SCROLL || player.InvList[i]._iMiscId == IMISC_SCROLLT)
-		    && player.InvList[i]._iSpell == player._pRSpell) {
+		    && player.InvList[i]._iSpell == player._pSpell) {
 			player.RemoveInvItem(i);
 			player.CalcScrolls();
 			return;

test/inv_test.cpp

@@ -198,7 +198,7 @@ TEST(Inv, RemoveScroll_inventory)
 
 	// Put a firebolt scroll into the inventory
 	Players[MyPlayerId]._pNumInv = 1;
-	Players[MyPlayerId]._pRSpell = static_cast<spell_id>(SPL_FIREBOLT);
+	Players[MyPlayerId]._pSpell = static_cast<spell_id>(SPL_FIREBOLT);
 	Players[MyPlayerId].InvList[0]._itype = ITYPE_MISC;
 	Players[MyPlayerId].InvList[0]._iMiscId = IMISC_SCROLL;
 	Players[MyPlayerId].InvList[0]._iSpell = SPL_FIREBOLT;