lda: Allow -f sender to omit domain.

Several people complained about the original enforcement of the presence of a
domain (added for v2.3.0) to be too restrictive. Apparently, this legitimately
happens with bounce messages on certain platforms.

src/lda/main.c

@@ -333,6 +333,7 @@ int main(int argc, char *argv[])
 			/* envelope sender address */
 			if (smtp_address_parse_path(ctx.pool, optarg,
 			    SMTP_ADDRESS_PARSE_FLAG_BRACKETS_OPTIONAL |
+				SMTP_ADDRESS_PARSE_FLAG_ALLOW_LOCALPART |
 				SMTP_ADDRESS_PARSE_FLAG_ALLOW_EMPTY,
 			    &mail_from, &errstr) < 0) {
 				i_fatal_status(EX_USAGE,