Assign read-only variables return code not usable inline

[Léa Gris]

https://ideone.com/iw2pSv

> #!/usr/bin/env bash
>  
> declare -r r
>  
> r=2 || exit 2
>  
> echo 'still there with $?='$?', after: r=2 || exit 2'
>  
> if ! r='hello'; then exit; fi
>  
> echo "still there with \$?=$?, after: if ! r='hello'; then exit; fi"
>  
> typeset -p r

Output:

> still there with $?=1, after: r=2 || exit 2
> still there with $?=1, after: if ! r='hello'; then exit; fi
> declare -r r


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