Fix missing condition for HW_GANBANTEIN (#6385)

Adds a condition for HW_GANBANTEIN since it's one of the skills that can be cast with no gemstone when equipped with Mistress Card.

src/map/skill.cpp

@@ -17078,7 +17078,7 @@ struct s_skill_condition skill_get_requirement(struct map_session_data* sd, uint
 					else {
 						if( sd->special_state.no_gemstone || (sc && sc->data[SC_INTOABYSS]) )
 						{	// All gem skills except Hocus Pocus and Ganbantein can cast for free with Mistress card -helvetica
-							if( skill_id != SA_ABRACADABRA )
+							if (skill_id != SA_ABRACADABRA && skill_id != HW_GANBANTEIN)
 		 						req.itemid[i] = req.amount[i] = 0;
 							else if( --req.amount[i] < 1 )
 								req.amount[i] = 1; // Hocus Pocus always use at least 1 gem