bugfix: imapserver "append" command: properly account for message size when bare newlines ("\n") are converted to crlf ("\r\n")

the original size, with bare newlines, was stored in the database, not the
actual adjusted file size. this caused failures when reading the message.

users may want to run "mox fixmsgsize <account>" if they imported messages from
another account over IMAP.

reported by daftaupe, thanks!

imapserver/server.go

@@ -2732,7 +2732,7 @@ func (c *conn) cmdAppend(tag, cmd string, p *parser) {
 				Received:      tm,
 				Flags:         storeFlags,
 				Keywords:      keywords,
-				Size:          size,
+				Size:          mw.Size,
 			}
 
 			mb.Add(m.MailboxCounts())