macrecovery: Fix ValueError

[mkorje]

When running the script in a builder, I was getting the error that Image verification failed. (Sign not allowed in string format specifier). If os.get_terminal_size().columns is less than 2 then the align left padding has a negative value, giving the error ValueError: Sign not allowed in string format specifier. I just added a check before the value's use to ensure that it isn't negative.

[mikebeaton]

Thank you for pointing out the issue when running headless.

Can you confirm that it works fine for you with my suggested additional commit?

[mkorje]

Yes, I can confirm that it works fine for me with your commit. Thank you for that.