dim: don't blow up on newline in Message-Id
Patchwork adds trailing newlines to long Message-Id header fields. message_get_id returns a string containing the newline, and dim_commit_add_tag blows up on that:
sed: -e expression #1, char 57: unknown command: `<'
Signed-off-by: Simon Ser contact@emersion.fr Closes: #17 (closed)