fix(3p/lisp/mime4cl): also default to :7BIT when decoding r/8974

Content-Transfer-Encoding should default to 7bit when it's not
given (RFC2045). MIME-PART already defaults to this when manually
constructing this, but MAKE-MIME-PART would always set it, so it would
sometimes be NIL which is incorrect. We now correctly fall back to :7bit
in this case.

Additionally, we make sure that KEYWORDIFY-ENCODING immediately returns
when it's given NIL.

Change-Id: I50f86dd649d83a4c3a8881d6e13dcada889d5521
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12857
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
Autosubmit: sterni <sternenseemann@systemli.org>

0 files changed, 0 insertions, 0 deletions