lineedit: don't block when looking for escape sequence in vi-mode

In vi-mode lineedit tries to detect some escape sequences.
After the ESC it reads the next character to check for certain
values.  This read should have a timeout or a user-entered ESC to
switch to command mode doesn't properly handle the next character.

Signed-off-by: Ron Yorston <rmy@tigress.co.uk>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>