[9729] Client not like vendor slot 0 so restore send slots counted from 1

This is must fix not selling first item in list by vendor.

src/game/ItemHandler.cpp

@@ -643,6 +643,12 @@ void WorldSession::HandleBuyItemInSlotOpcode( WorldPacket & recv_data )
 
     recv_data >> vendorguid >> item  >> slot >> bagguid >> bagslot >> count;
 
+    // client side expected counting from 1, and we send to client vendorslot+1 already
+    if (slot > 0)
+        --slot;
+    else
+        return;                                             // cheating
+
     uint8 bag = NULL_BAG;                                   // init for case invalid bagGUID
 
     // find bag slot by bag guid
@@ -679,6 +685,12 @@ void WorldSession::HandleBuyItemOpcode( WorldPacket & recv_data )
 
     recv_data >> vendorguid >> item >> slot >> count >> unk1;
 
+    // client side expected counting from 1, and we send to client vendorslot+1 already
+    if (slot > 0)
+        --slot;
+    else
+        return;                                             // cheating
+
     GetPlayer()->BuyItemFromVendorSlot(vendorguid, slot, item, count, NULL_BAG, NULL_SLOT);
 }
 
@@ -750,7 +762,7 @@ void WorldSession::SendListInventory(uint64 vendorguid)
                 // reputation discount
                 uint32 price = uint32(floor(pProto->BuyPrice * discountMod));
 
-                data << uint32(vendorslot);
+                data << uint32(vendorslot +1);              // client size expected counting from 1
                 data << uint32(crItem->item);
                 data << uint32(pProto->DisplayInfoID);
                 data << uint32(crItem->maxcount <= 0 ? 0xFFFFFFFF : pCreature->GetVendorItemCurrentCount(crItem));

src/shared/revision_nr.h

@@ -1,4 +1,4 @@
 #ifndef __REVISION_NR_H__
 #define __REVISION_NR_H__
- #define REVISION_NR "9728"
+ #define REVISION_NR "9729"
 #endif // __REVISION_NR_H__