hterm: Fix concealed/invisible text for default background.
hterm: Fix concealed/invisible text for default background.

The output of

    printf '\e[0;8mYou should not see this.\e[0m'

should not be visible.

Change-Id: I3987648f091333fde91a133e78e8eb487ff5e277
Reviewed-on: https://chromium-review.googlesource.com/259382
Reviewed-by: Rob Ginda <4419ac4e35d191308e944202d542b192188656d1@chromium.org>
Tested-by: Rob Ginda <4419ac4e35d191308e944202d542b192188656d1@chromium.org>

hernad/libapps,hernad/libapps,hernad/libapps,hernad/libapps