unbreak deskutils/gucharmap after update of textproc/UCD

gen-guch-unicode-tables.pl generated a unicode-versions.h file with
all unicode versions found in UCD's DerivedAge.txt file - regardless
of wether gucharmap itself supports that unicode version. This makes
sure that codepoints with a higer unicode version than supported are
skipped.

PR: 228830
Approved by: maintainer (pi)