Darboux transformation and analytic solutions of the discrete <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si29.gif" display="inline" overflow="scroll"><mml:mi mathvariant="script">P</mml:mi><mml:mi mathvariant="script">T</mml:mi></mml:math>-symmetric nonlocal nonlinear Schrödinger equation