Corrected Graffiti removing all units (fixes #1263)

* Graffiti will no longer remove all units of the Rogue class.
* Graffiti will now fail to cast again if a Graffiti already exists on the map.
* Graffiti should only be removed on map changes, but Remover/Cleaner still removes it (custom) since the skill was never officially implemented.

src/map/skill.c

@@ -11638,7 +11638,6 @@ int skill_castend_pos2(struct block_list* src, int x, int y, uint16 skill_id, ui
 			clif_skill_poseffect(src,skill_id,skill_lv,x,y,tick);
 		break;
 	case RG_GRAFFITI:			/* Graffiti [Valaris] */
-		skill_clear_unitgroup(src);
 		skill_unitsetting(src,skill_id,skill_lv,x,y,0);
 		flag|=1;
 		break;
@@ -11665,7 +11664,7 @@ int skill_castend_pos2(struct block_list* src, int x, int y, uint16 skill_id, ui
 		break;
 	case RG_CLEANER: // [Valaris]
 		i = skill_get_splash(skill_id, skill_lv);
-		map_foreachinarea(skill_graffitiremover,src->m,x-i,y-i,x+i,y+i,BL_SKILL);
+		map_foreachinarea(skill_graffitiremover,src->m,x-i,y-i,x+i,y+i,BL_SKILL,1);
 		break;
 
 	case SO_WARMER:
@@ -14785,6 +14784,12 @@ bool skill_check_condition_castbegin(struct map_session_data* sd, uint16 skill_i
 	}
 	// perform skill-specific checks (and actions)
 	switch( skill_id ) {
+		case RG_GRAFFITI:
+			if (map_foreachinmap(skill_graffitiremover,sd->bl.m,BL_SKILL,0)) { // If a previous Graffiti exists skill fails to cast.
+				clif_skill_fail(sd,skill_id,USESKILL_FAIL_LEVEL,0);
+				return false;
+			}
+			break;
 		case SO_SPELLFIST:
 			if(sd->skill_id_old != MG_FIREBOLT && sd->skill_id_old != MG_COLDBOLT && sd->skill_id_old != MG_LIGHTNINGBOLT) {
 				clif_skill_fail(sd,skill_id,USESKILL_FAIL_LEVEL,0);
@@ -16931,15 +16936,19 @@ struct skill_unit_group *skill_locate_element_field(struct block_list *bl)
 int skill_graffitiremover(struct block_list *bl, va_list ap)
 {
 	struct skill_unit *unit = NULL;
+	int remove = va_arg(ap, int);
 
-	nullpo_ret(bl);
-	nullpo_ret(ap);
+	nullpo_retr(0, bl);
+	nullpo_retr(0, ap);
 
 	if (bl->type != BL_SKILL || (unit = (struct skill_unit *)bl) == NULL)
 		return 0;
 
-	if ((unit->group) && (unit->group->unit_id == UNT_GRAFFITI))
-		skill_delunit(unit);
+	if ((unit->group) && (unit->group->unit_id == UNT_GRAFFITI)) {
+		if (remove == 1)
+			skill_delunit(unit);
+		return 1;
+	}
 
 	return 0;
 }