scrmap is only used in the one compilation unit in all cases, make it static
rather than extern'ing it. There's little benefit, but it's easy to do.
It's unclear how this hasn't failed many builds before now, since it should
have cropped up sometime around deeper hierarchies getting a default WARNS.
MFC after: 3 days
but those maps also used as backward maps for Paste, so space becomes mapped
to last non-existen character on Paste as result.
Fix it by mapping non-existen characters to another non-existen one, i.e. to
0x00, so unused 0x00 can be backward-mapped to some junk without real harm.
Pointed by: Alexander Kabaev <ak03@gte.com>
