Fixed monster unlocking target during cast (fixes #1134)

* Monsters will no longer unlock their target when they use a skill that has a cast time on a target they need to chase

src/map/mob.c

@@ -1761,7 +1761,8 @@ static bool mob_ai_sub_hard(struct mob_data *md, unsigned int tick)
 	{
 		if (DIFF_TICK(md->ud.canmove_tick, tick) <= MIN_MOBTHINKTIME && DIFF_TICK(md->ud.canact_tick, tick) < -MIN_MOBTHINKTIME*IDLE_SKILL_INTERVAL) 
 		{ //Only use skill if able to walk on next tick and not used a skill the last second
-			mobskill_use(md, tick, -1);
+			if (mobskill_use(md, tick, -1))
+				return true;
 		}
 	}