Corrected NPC_DARKBREATH formula (#7285)

* Corrected NPC_DARKBREATH formula
Fixes #7284

* Update src/map/battle.cpp

Co-authored-by: Pokye <98105181+Pokye@users.noreply.github.com>

* Update src/map/battle.cpp

Co-authored-by: Lemongrass3110 <lemongrass@kstp.at>

* Added renewal logic

* now uses only one formula for both modes

---------

Co-authored-by: Lemongrass3110 <lemongrass@kstp.at>
Co-authored-by: Pokye <98105181+Pokye@users.noreply.github.com>

src/map/battle.cpp

@@ -7246,7 +7246,7 @@ struct Damage battle_calc_magic_attack(struct block_list *src,struct block_list
 				}
 				break;
 			case NPC_DARKBREATH:
-				ad.damage = tstatus->hp * (skill_lv <= 5 ? 100 / (2 * 6 - skill_lv) : 50) / 100;
+				ad.damage = tstatus->hp * (skill_lv <= 5 ? 100 / (2 * (6 - skill_lv)) : 50) / 100;
 				break;
 			case PF_SOULBURN:
 				ad.damage = tstatus->sp * 2;