freqinput needs a check if oldchk is set and guess value if unset

[polyluxus]

Using g16.freqinput on a file where no chk statement is present will produce a new file without oldchk statement. Since the input depends on the presence of this file, Gaussian will abort with an error.

If there is no chk statement to construct the oldchk statement from, test for a checkpoint file with the same basename and use this instead.

This is especially an issue, since inputfiles submitted with g16.submit of this bundle don't necessary need a chk statement, since the script will automatically add it. Using the wrong inputfile will then recreate this error.