Fixed bugreport:4109 battle ground guardians will now follow nearby allies when no foes are in range.

git-svn-id: https://svn.code.sf.net/p/rathena/svn/trunk@16208 54d463be-8e91-2dee-dedb-b68131a5f0ec

src/map/mob.c

@@ -1122,6 +1122,22 @@ static int mob_ai_sub_hard_changechase(struct block_list *bl,va_list ap)
 	return 1;
 }
 
+/*==========================================
+ * finds nearby bg ally for guardians looking for users to follow.
+ *------------------------------------------*/
+static int mob_ai_sub_hard_bg_ally(struct block_list *bl,va_list ap) {
+	struct mob_data *md;
+	struct block_list **target;
+	
+	nullpo_ret(bl);
+	md=va_arg(ap,struct mob_data *);
+	target= va_arg(ap,struct block_list**);
+		
+	if( status_check_skilluse(&md->bl, bl, 0, 0) && battle_check_target(&md->bl,bl,BCT_ENEMY)<=0 ) {
+		(*target) = bl;
+	}
+	return 1;
+}
 
 /*==========================================
  * loot monster item search
@@ -1528,6 +1544,18 @@ static bool mob_ai_sub_hard(struct mob_data *md, unsigned int tick)
 	if (!tbl) { //No targets available.
 		if (mode&MD_ANGRY && !md->state.aggressive)
 			md->state.aggressive = 1; //Restore angry state when no targets are available.
+		
+		/* bg guardians follow allies when no targets nearby */
+		if( md->bg_id && mode&MD_CANATTACK ) {
+			if( md->ud.walktimer != INVALID_TIMER )
+				return true;/* we are already moving */
+			map_foreachinrange (mob_ai_sub_hard_bg_ally, &md->bl, view_range, BL_PC, md, &tbl, mode);
+			if( tbl ) {
+				if( distance_blxy(&md->bl, tbl->x, tbl->y) <= 3 || unit_walktobl(&md->bl, tbl, 1, 1) )
+					return true;/* we're moving or close enough don't unlock the target. */
+			}
+		}
+		
 		//This handles triggering idle walk/skill.
 		mob_unlocktarget(md, tick);
 		return true;