Fixes undefined 'USER_ID' usage

[vpetersson]

The variable $USER_ID was defined but then in the actual Docker run, only USER_ID was passed on, which broke the script.

(Also includes a minor white space cleanup)

[lmbarros]

Hi @vpetersson, thanks for looking into this. I believe, though, that the script is correct at that point. As per the Docker docs, "If the operator names an environment variable without specifying a value, then the current value of the named variable is propagated into the container’s environment".

[vpetersson]

Hmm, it didn't work like that for me. Before this fix, I got the following:

Building tool, please wait...
[LOG]Unwraping balena image from the provided balena image flasher...
[LOG]Changing file permissions.
chown: cannot access '': No such file or directory

This was on:

$ docker --version
Docker version 20.10.7, build 20.10.7-0ubuntu5~20.04.2

[lmbarros]

The user ID is getting to the script running on the container. The error happens because the file name is missing; we are running something like chown 1234:1234 "", hence the "cannot access ''" message. With your change, I believe the USER_ID variable will be unset in the container. The error vanishes because of the if [ ! -z "$USER_ID" ] right before the point where we call chown.

(Now, of course you have hit a bug, which I believe is for different reasons: #13).

[vpetersson]

I stand corrected. You're right @lmbarros. I wasn't aware of this feature. Good one!