eml: each_part: single part $idx is 1

Instead of counts starting at 0, we start the single-part
message at 1 like we do with subparts of a multipart message.
This will make it easier to map offsets for "BODY[$SECTION]"
when using IMAP FETCH, since $SECTION must contain non-zero
numbers according to RFC 3501.

This doesn't make any difference for WWW URLs, since single part
messages cannot have downloadable attachments.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/PublicInbox/MsgIter.pm b/lib/PublicInbox/MsgIter.pm
index 5ec2a4d9..bb1dfead 100644
--- a/lib/PublicInbox/MsgIter.pm
+++ b/lib/PublicInbox/MsgIter.pm
@@ -34,7 +34,7 @@ sub em_each_part ($$;$$) {
                         }
                 }
         } else {
-                $cb->([$mime, 0, 0], $cb_arg);
+                $cb->([$mime, 0, 1], $cb_arg);
         }
 }