[Bots] Restore old buff overwrite blocking (#4832)

- [#4756](https://github.com/EQEmu/Server/pull/4756) changed the way overwriting worked for buffs. It allowed stronger spells to overwrite lesser spells if they were already on the target.
- However, this is a positive change but has its drawbacks with spells of similar value. It could cause an endless buff loop where they constantly replaced one another.

Overall, the con of endless buffing outweighs the benefit of automatic overwriting lesser spells and the control should be left to only spell lists via `^spells` for bot owners as it was before to determine which buffs bots will cast.

zone/bot.cpp

@@ -9738,7 +9738,7 @@ bool Bot::CastChecks(uint16 spell_id, Mob* tar, uint16 spell_type, bool precheck
 			)
 		)
 		&&
-		tar->CanBuffStack(spell_id, GetLevel(), false) < 0
+		tar->CanBuffStack(spell_id, GetLevel(), true) < 0
 	) {
 		LogBotSpellChecksDetail("{} says, 'Cancelling cast of {} on {} due to !CanBuffStack.'", GetCleanName(), GetSpellName(spell_id), tar->GetCleanName());
 		return false;