Frequencies are sorted as strings, not numercially

[c-feldmann]

As the title says:
When opening a file with vibrational modes and sorting them, the frequencies are sorted as sting not in numerical (a/de)scending order. I'm using 1.2.0 on Ubuntu, installed form the official repositories.
I hope this helps to fix it. When you need a file to reproduce my problem, please let me know.