VIP Drop calculation correction

* Fixes #2247.
* Adjusted the drop rate to properly float the value before converting to integer.
Thanks to @talesvalente!

src/map/mob.c

@@ -2659,7 +2659,7 @@ int mob_dead(struct mob_data *md, struct block_list *src, int type)
 				drop_rate = i32max(drop_rate, cap_value(drop_rate_bonus, 0, 9000));
 
 				if (pc_isvip(sd)) { // Increase item drop rate for VIP.
-					drop_rate += (int)(0.5 + (drop_rate * battle_config.vip_drop_increase) / 100);
+					drop_rate += (int)(0.5 + drop_rate * battle_config.vip_drop_increase / 100.);
 					drop_rate = min(drop_rate,10000); //cap it to 100%
 				}
 			}