Fixes typo in atcommand.cpp that makes atcommand @accept after duel cannot be used because of limit player reached. (#2778)

src/map/atcommand.cpp

@@ -8419,7 +8419,7 @@ ACMD_FUNC(accept)
 		return 0;
 	}
 
-	if( duel_check_player_limit( duel_get_duelid( sd->duel_invite ) ) )
+	if( !duel_check_player_limit( duel_get_duelid( sd->duel_invite ) ) )
 	{
 		clif_displaymessage(fd, msg_txt(sd,351)); // "Duel: Limit of players is reached."
 		return 0;