Corrected Shadow Warrior double attack rate (#2988)

* Fixes #2968.
* The rate of double attack should match the rate of Thief's Double Attack even levels.
* Confirmed that the double attack bonus does not work when weapons are not equipped.
Thanks to @redlightliu!

src/map/battle.cpp

@@ -3322,12 +3322,16 @@ static struct Damage battle_calc_multi_attack(struct Damage wd, struct block_lis
 	if( sd && !skill_id ) {	// if no skill_id passed, check for double attack [helvetica]
 		short i;
 		if( ( ( skill_lv = pc_checkskill(sd,TF_DOUBLE) ) > 0 && sd->weapontype1 == W_DAGGER )
-			|| ( sd->bonus.double_rate > 0 && sd->weapontype1 != W_FIST ) //Will fail bare-handed
-			|| ( sc && sc->data[SC_KAGEMUSYA] && sd->weapontype1 != W_FIST )) // Need confirmation
+			|| ( sd->bonus.double_rate > 0 && sd->weapontype1 != W_FIST ) // Will fail bare-handed
+			|| ( sc && sc->data[SC_KAGEMUSYA] && sd->weapontype1 != W_FIST )) // Will fail bare-handed
 		{	//Success chance is not added, the higher one is used [Skotlex]
-                        int max_rate = max(5*skill_lv,sd->bonus.double_rate);
-                        if(sc && sc->data[SC_KAGEMUSYA]) max_rate= max(max_rate,sc->data[SC_KAGEMUSYA]->val1*3);
-                        
+			int max_rate = 0;
+
+			if (sc && sc->data[SC_KAGEMUSYA])
+				max_rate = sc->data[SC_KAGEMUSYA]->val1 * 10; // Same rate as even levels of TF_DOUBLE
+			else
+				max_rate = max(5 * skill_lv, sd->bonus.double_rate);
+
 			if( rnd()%100 < max_rate ) {
 				wd.div_ = skill_get_num(TF_DOUBLE,skill_lv?skill_lv:1);
 				wd.type = DMG_MULTI_HIT;