Core/Group: Do not allow a player to invite himself

Do not allow a player to invite himself in group.
Fix an edge case when inviting another player that would cause a crash.
Fix #17664

src/server/game/Handlers/GroupHandler.cpp

@@ -114,6 +114,13 @@ void WorldSession::HandleGroupInviteOpcode(WorldPacket& recvData)
         return;
     }
 
+    // player trying to invite himself (most likely cheating)
+    if (player == GetPlayer())
+    {
+        SendPartyResult(PARTY_OP_INVITE, membername, ERR_BAD_PLAYER_NAME_S);
+        return;
+    }
+
     // restrict invite to GMs
     if (!sWorld->getBoolConfig(CONFIG_ALLOW_GM_GROUP) && !GetPlayer()->IsGameMaster() && player->IsGameMaster())
     {
@@ -256,6 +263,7 @@ void WorldSession::HandleGroupInviteOpcode(WorldPacket& recvData)
         }
         if (!group->AddInvite(player))
         {
+            group->RemoveAllInvites();
             delete group;
             return;
         }