Gnus nnml should avoid crashing on some invalid headers

Gnus nnml should avoid crashing on some invalid headers

This upstream patch has been incorporated to fix the problem:

  Fix storing email into nnmail by Gnus

  * lisp/gnus/nnml.el (nnml--encode-headers): Wrap
  'rfc2047-encode-string' calls with 'ignore-errors', to avoid
  disrupting email workflows due to possibly-invalid headers.
  Reported by Florian Weimer <fweimer@redhat.com>.

Origin: upstream, commit: 23f7c9c2a92e4619b7c4d2286d4249f812cd695d
Bug-Debian: https://bugs.debian.org/1033397
Forwarded: not-needed