Program fails to start again after exiting once

[ken-ruster]

After starting the program once, entering 2 drugs and 2 profiles, then not saving any of the information and quitting using the inbuilt bye command, subsequent attempts to start the program return an error where it fails to initialise.

Able to start the program normally once the files users.txt and drugs.txt are deleted, without the data.

As a result users may be unable to resume with their saved data when starting a new session.