Fix Set/Reset Screen Mode escape sequences

This makes csi_sequence() ignore Set/Reset Screen Mode escape sequence
commands line escape.js does.

There's two potential problems:

  - The "line wrapping" feature is always enabled. There's no way for
    an escape sequence to disable it.

  - We don't handle the mysterious Esc[?33h escape sequence that seems
    to pop up in various Blocktronics artpacks.

Signed-off-by: Pekka Enberg <penberg@kernel.org>