Hi! Done that recently on my server.
skill.cpp
case GS_DISARM: skill_strip_equip(src, bl, skill_id, skill_lv); clif_skill_nodamage(src,bl,skill_id,skill_lv,1); break;
To
case GS_DISARM:
if( skill_strip_equip(src, bl, skill_id, skill_lv) )
clif_skill_nodamage(src,bl,skill_id,skill_lv,1);
break;