vt: make sure displayed double-width characters are remembered as such

And to do so we ensure the Unicode screen buffer is initialized when
double-width characters are encountered.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Link: https://lore.kernel.org/r/20250507141535.40655-3-nico@fluxnic.net


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>