connect.c: fix leak in handle_ssh_variant

When we see an error from split_cmdline(), we exit the
function without freeing the copy of the command string we
made.

This was sort-of introduced by 22e5ae5c8 (connect.c: handle
errors from split_cmdline, 2017-04-10). The leak existed
before that, but before that commit fixed the bug, we could
never trigger this else clause in the first place.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

connect.c

@@ -738,8 +738,10 @@ static void handle_ssh_variant(const char *ssh_command, int is_cmdline,
 			 * any longer.
 			 */
 			free(ssh_argv);
-		} else
+		} else {
+			free(p);
 			return;
+		}
 	}
 
 	if (!strcasecmp(variant, "plink") ||