tr: fix complemented class truncation ordering

[can1357]

uutils tr applies the complemented-character-class guard before --truncate-set1, then truncates the translated set afterward. That allows -ct to translate only a subset of complemented bytes, while GNU rejects this shape instead of allowing partial mapping.

Reproduction Steps

printf A | tr -ct '[:digit:]' X
# Expected (GNU): exit 1 with "when translating with complemented character classes, string2 must map all characters in the domain to one"
# Actual (uutils): exit 0 & outputs "A"

Impact

This breaks GNU compatibility and weakens sanitization pipelines that rely on tr -ct to enforce translation coverage. Inputs that should be rejected can be accepted with under-filtered output.