Fixed some more server crashes

Thanks to @functor-x

src/map/clif.cpp

@@ -19730,6 +19730,11 @@ void clif_parse_merge_item_req(int fd, struct map_session_data* sd) {
 
 	for (i = 0, j = 0; i < n; i++) {
 		unsigned short idx = RFIFOW(fd, info->pos[1] + i*2) - 2;
+
+		if( idx < 0 || idx >= MAX_INVENTORY ){
+			return;
+		}
+
 		if (!clif_merge_item_check((id = sd->inventory_data[idx]), &sd->inventory.u.items_inventory[idx]))
 			continue;
 		indexes[j] = idx;

src/map/skill.cpp

@@ -20015,6 +20015,11 @@ int skill_elementalanalysis(struct map_session_data* sd, int n, uint16 skill_lv,
 		struct item tmp_item;
 
 		idx = item_list[i*2+0]-2;
+
+		if( idx < 0 || idx >= MAX_INVENTORY ){
+			return 1;
+		}
+
 		del_amount = item_list[i*2+1];
 
 		if( skill_lv == 2 )
@@ -20088,6 +20093,11 @@ int skill_changematerial(struct map_session_data *sd, int n, unsigned short *ite
 					if( skill_produce_db[i].mat_id[j] > 0 ) {
 						for( k = 0; k < n; k++ ) {
 							int idx = item_list[k*2+0]-2;
+
+							if( idx < 0 || idx >= MAX_INVENTORY ){
+								return 0;
+							}
+
 							nameid = sd->inventory.u.items_inventory[idx].nameid;
 							amount = item_list[k*2+1];
 							if( nameid > 0 && sd->inventory.u.items_inventory[idx].identify == 0 ){