[PATCH 3/3] lib-sieve: edit_mail_headers_parse() - Fix info leak via NUL-truncated...

[PATCH 3/3] lib-sieve: edit_mail_headers_parse() - Fix info leak via NUL-truncated header copy

i_strndup() stops at the first NUL byte, so embedded NULs caused field->data
to be shorter than field->size. This left stale heap data readable past the
copied content when callers treat data+body_offset as a string.

Adds a test-edit-mail unit test and a sieve testsuite case that both
exercise edit_mail_headers_parse() with a NUL byte embedded in a header
value. The unit test memcmp-verifies that the bytes after the NUL are
preserved; the sieve test triggers an invalid heap read detectable by
valgrind under the old code.

Gbp-Pq: Name 0003-lib-sieve-edit_mail_headers_parse-Fix-info-leak-via-.patch