found with cppcheck 2.1

cc: @gtribello

[multicolvar/InPlaneDistances.cpp:110] (warning) :nullPointerRedundantCheck: Either the condition 'bt' is redundant or there is possible null pointer dereference: bt.

This looks like it might be a real bug! Should be checked and potentially backported if it's a bug fix.

#582

#582

Fixes #582

Clarify that the energy CV is actually the potential energy

Make sure that output files are written out at the final step. Should fix issues with restarting reported by @PabloPiaggi

cc: @gtribello

I think this has been here since the beginning, the effect is measurable