imapc: Don't trust mail stream to have correct CRLFs

It's not that expensive to just recalculate them. If they're not correct in
the stream, it can result in e.g. truncated emails due to wrong virtual_size
being used in body_size calculation. The wrong CRLFs can especially happen
if plugins modify the stream in istream_opened() hook.

src/lib-storage/index/imapc/imapc-mail-fetch.c

@@ -589,12 +589,15 @@ void imapc_mail_init_stream(struct imapc_mail *mail)
 	   smaller than the fetched message header. In this case change the
 	   size as well, otherwise reading via istream-mail will fail. */
 	if (mail->body_fetched || imail->data.physical_size < size) {
-		if (mail->body_fetched)
+		if (mail->body_fetched) {
 			imail->data.inexact_total_sizes = FALSE;
+			/* Don't trust any existing virtual_size. Also don't
+			   set it to size, because there's no guarantees about
+			   the content having proper CRLF newlines, especially
+			   not if istream_opened() has changed the stream. */
+			imail->data.virtual_size = (uoff_t)-1;
+		}
 		imail->data.physical_size = size;
-		/* we'll assume that the remote server is working properly and
-		   sending CRLF linefeeds */
-		imail->data.virtual_size = size;
 	}
 
 	imail->data.stream_has_only_header = !mail->body_fetched;