[BUG] Changing default user shell renders LinuxGSM inoperable

## User Story

It looks like LinuxGSM does not take kindly to changing the users default shell.
Example: the vhserver user has default shell `/usr/bin/fish` set when running `wget -O linuxgsm.sh https://linuxgsm.sh && chmod +x linuxgsm.sh && bash linuxgsm.sh vhserver` and `./vhserver install`. Starting and stopping the server works just fine using `./vhserver start/stop`. Now if we change the shell to bash for example `chsh -s /bin/bash`. `./vhserver stop` or `/vhserver details` doesn't seem to work at all anymore whereas `start` does start the server but the shell hangs with output `[ .... ] Starting vhserver: `.

## Basic info

* **Distro:** Ubuntu 20.04
* **Game:** Valheim but not really relevant I assume
* **Command:** any
* **LinuxGSM version:** v20.1.3

## Further Information

## To Reproduce

Steps to reproduce the behaviour:

1. Install a valheim server for example with default shell set to `/usr/bin/fish` for the `vhserver` user
2. Start stop the server using `./vhserver start` `./vhserver stop`
3. Change the default shell using `chsh -s /bin/bash` to bash
4. Use `exit` to quit the current shell and login again using `su - vhserver`
4. Try to start/stop the server now using the commands above in bash

## Expected behaviour

Same as when using /usr/bin/fish.