g_traj -f file.xtc -ov writes an empty file (silently?)
Generally such tools should warn the user that the input file does not contain the kind of data they seek to operate on, rather than writing an empty file (silently or not).
Disallow extracting V/F from XTC files in g_traj
We now issue a fatal error if the user asks for velocities or
forces to be written to as output from g_traj when the input
XTC file does not contain these quantities.