Fix OSC sequence parsing

printf '\033]2;aaa\033bbb' prints bbb
printf '\033]2;aaa\033\\bbb' prints bbb
printf '\033]2;aaa\033' prints nothing;

title is changed when next character is received.

printf '\033]2;aaa\033\\' prints nothing
printf '\033]2;aaa\007bbb' prints bbb
printf '\033]2;aaa\007\\bbb' prints \bbb
printf '\033]2;a\ra\na\033bbb' prints bbb
printf '\033]2;a\ra\na\033\\bbb' prints bbb
printf '\033]2;a\ra\na\007bbb' prints bbb

In each case the title is set to aaa

BUG: 231405
FIXED-IN: 19.12.0