Fixed UNT_JACK_FROST_NOVA and UNT_GROUND_GRAVITATION (#8619)

* Added missing UNT_JACK_FROST_NOVA and UNT_GROUND_GRAVITATION in skill_unit_onplace_timer
(damage over time were missing)

src/map/skill.cpp

@@ -16035,6 +16035,8 @@ int skill_unit_onplace_timer(struct skill_unit *unit, struct block_list *bl, t_t
 		case UNT_SOLIDTRAP:
 		case UNT_SWIFTTRAP:
 		case UNT_FLAMETRAP:
+		case UNT_GROUND_GRAVITATION:
+		case UNT_JACK_FROST_NOVA:
 			skill_attack(skill_get_type(sg->skill_id),ss,&unit->bl,bl,sg->skill_id,sg->skill_lv,tick,0);
 			break;