misc: Set default port to 22 in ssh_path_expand_escape()

Fixes, among others, ProxyCommand with %p when no port is used on
commandline or config file, thus using the default port.

Fixes T94

Signed-off-by: Alex Hermann <alex@hexla.nl>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
(cherry picked from commit 23f60a56f3)

src/misc.c

@@ -778,7 +778,10 @@ char *ssh_path_expand_escape(ssh_session session, const char *s) {
                 if (session->opts.port < 65536) {
                     char tmp[6];
 
-                    snprintf(tmp, sizeof(tmp), "%u", session->opts.port);
+                    snprintf(tmp,
+                             sizeof(tmp),
+                             "%u",
+                             session->opts.port > 0 ? session->opts.port : 22);
                     x = strdup(tmp);
                 }
                 break;