Fail at check_loop_device: device node doesn't exist and `$LOOP=`

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      1. What happened?

I did confirm this problem on the main branch

~_{Trying to build armbian on gentoo with docker. Targeting bigtreetech CB2 from https://github.com/bigtreetech/build/tree/CB2}~

~_{The fork isn't far behind the main branch, at least in terms of the compile script.}~

The problem seems to be that the script is looking for a loop device, but there aren't any that match a pattern, yet the loop exits on the first iteration with a false positive and empty `LOOP` variable.

paste.armbian.com/log returns a 500 status code, putting the log here:
[log-build-3ebc61fd-016c-4aa1-9a41-00194251ff89.log.ans.txt](https://github.com/armbian/build/files/15264700/log-build-3ebc61fd-016c-4aa1-9a41-00194251ff89.log.ans.txt)

Also, the log with docker prefix, because the script decided to use docker automatically:
[log-docker-3ebc61fd-016c-4aa1-9a41-00194251ff89.log.ans.txt](https://github.com/armbian/build/files/15264734/log-docker-3ebc61fd-016c-4aa1-9a41-00194251ff89.log.ans.txt)

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      1. How to reproduce?

(May get updated)

1. Checkout the repo
2. Run `./compile.sh`
3. Make all the selections and wait until the failing point

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      1. Branch

main (main development branch)

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      1. On which host OS are you running the build script and observing this problem?

Other

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      1. Are you building on Windows WSL2?

• [ ] Yes, my Ubuntu/Debian/OtherOS is running on WSL2

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      1. Relevant log URL

{message:Error adding document.}

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      1. Code of Conduct

• [X] I agree to follow this project's Code of Conduct

Raised by: https://github.com/JohnTheCoolingFan

https://github.com/armbian/build/issues/6568