Hong Kong police officers have received top-level approval to carry extendable batons during off-hours to execute “constabulary duties”, according to an internal memo issued by the force.The approval was given after the force examined the possibility of issuing handguns to officers following a recent knife attack on an off-duty officer and online threats, including calls for attacks against them.The Post was told that the 31,000-strong force dropped the handguns plan because “there aren’t…