Prevent theoretical NULL deref in throughlocal_sftp.

Coverity CID 405019, although at the moment it's not reachable. ok djm@

Author: daztucker

usr.bin/ssh/scp.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: scp.c,v 1.261 2024/06/26 23:14:14 deraadt Exp $ */
+/* $OpenBSD: scp.c,v 1.262 2025/03/19 06:11:15 dtucker Exp $ */
 /*
  * scp - secure remote copy.  This is basically patched BSD rcp which
  * uses ssh to do the data transfer (instead of using rcmd).
@@ -1024,7 +1024,7 @@ toremote(int argc, char **argv, enum scp_mode_e mode, char *sftp_direct)
 		}
 		if (host && throughlocal) {	/* extended remote to remote */
 			if (mode == MODE_SFTP) {
-				if (remin == -1) {
+				if (remin == -1 || conn == NULL) {
 					/* Connect to dest now */
 					conn = do_sftp_connect(thost, tuser,
 					    tport, sftp_direct,