DEBUG: init: report invalid characters in debug description strings

DEBUG: init: report invalid characters in debug description strings

It's easy to leave some trailing \n or even other characters that can
mangle the debug output. Let's verify at boot time that the debug sections
are clean by checking for chars 0x20 to 0x7e inclusive. This is very simple
to do and it managed to find another one in a multi-line message:

  [WARNING]  (23696) : Invalid character 0x0a at position 96 in description string at src/cli.c:2516 _send_status()

This way new offending code will be spotted before being committed.