in hmc_tm, correctly pass acctest to update_tm even for trajectory 0

fixes a silly bug introduced by me when i made the initial trajectory number consistent across parameter values. At the time the first trajectory would be 0 if "readin" was specified but .nstore_counter would fail to be read. Otherwise it would start at 1. With my changes from a couple of months ago it now always starts at 0. I overlooked, however, that update_tm is called with acctest a comparison between Ntherm and trajcounter, which would evaluate to 0 for trajectory 0 and Ntherm 0, thereby skipping the acceptance test in the first trajectory.