11_terminal: Make axzsh_is_widechar_terminal() safer
11_terminal: Make axzsh_is_widechar_terminal() safer

Sometimes there were leftover artifacts of the escape sequence visible
in screen(1) and tmux(1), but not always. Anyways, with the splitted
echoing of the escape sequence, at least I wasn't able to reproduce it
any more, so hopefully this fixes the problem for everybody.

alexbarton/ax-zsh