[Bots] Fix rule Bots:FinishBuffing (#4788)

zone/bot.cpp

@@ -9533,7 +9533,14 @@ bool Bot::CastChecks(uint16 spell_id, Mob* tar, uint16 spell_type, bool precheck
 		return false;
 	}
 
-	if (!BotHasEnoughMana(spell_id)) {
+	if (
+		!BotHasEnoughMana(spell_id) &&
+		(
+			!RuleB(Bots, FinishBuffing) ||
+			IsEngaged() ||
+			IsBotBuffSpellType(spell_type)
+		)
+	) {
 		LogBotSpellChecksDetail("{} says, 'Cancelling cast of {} due to !BotHasEnoughMana.'", GetCleanName(), GetSpellName(spell_id));
 		return false;
 	}

zone/botspellsai.cpp

@@ -562,7 +562,9 @@ bool Bot::AIDoSpellCast(int32 i, Mob* tar, int32 mana_cost, uint32* oDontDoAgain
 	// Allow bots to cast buff spells even if they are out of mana
 	if (
 		RuleB(Bots, FinishBuffing) &&
-		manaCost > hasMana && AIBot_spells[i].type == BotSpellTypes::Buff
+		manaCost > hasMana &&
+		!IsEngaged() &&
+		IsBotBuffSpellType(AIBot_spells[i].type)
 	) {
 		SetMana(manaCost);
 	}