qpe: Convert a debug fprintf() to LOGGER_log()

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>
Fix the insertion of BASE64 encoded HTML

Commit 12f7491 )"Introduce --{pretext,disclaimer}-html-b64= options")
added the ability to insert BASE64 encoded HTML into text/html BASE64
encoded MIME parts.

This was very broken. I don't know how it was working, but it was when I
tested it!

Issues included:

- Missing MIME boundary when passing data to
  AM_add_disclaimer_insert_html

- The logic in AM_add_disclaimer_insert_html was wrong for dealing with
  BASE64 html insertion.

- Excess left over code in AM_insert_HTML_disclaimer_into_segment64 from
  its copy and paste creation.

- MIME boundaries appearing in the wrong places due to the above.

Anyway, (hopefully) fix'd it all up and it made
AM_add_disclaimer_insert_html and
AM_insert_HTML_disclaimer_into_segment64 simpler to boot. Win win.

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>
Hook up --{pretext,disclaimer}-html-b64= to non multi-part

Commit 12f7491 ("Introduce --{pretext,disclaimer}-html-b64= options")
added the ability to insert BASE64 encoded HTML into text/html BASE64
encoded MIME parts.

This makes this work for non multi-part messages.

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>