xenstore: handle daemon creation errors

In rare cases, the path to the daemon socket cannot be created as it is
longer than PATH_MAX. Instead of failing with a NULL pointer dereference,
terminate the application with an error message.

This bug was discovered and resolved using Coverity Static Analysis
Security Testing (SAST) by Synopsys, Inc.

Signed-off-by: Norbert Manthey <nmanthey@amazon.de>
Reviewed-by: Thomas Friebel <friebelt@amazon.de>
Reviewed-by: Julien Grall <jgrall@amazon.co.uk>
Reviewed-by: Juergen Gross <jgross@suse.com>

tools/xenstore/xenstored_core.c

@@ -2005,6 +2005,9 @@ static void init_sockets(void)
 	struct sockaddr_un addr;
 	const char *soc_str = xs_daemon_socket();
 
+	if (!soc_str)
+		barf_perror("Failed to obtain xs domain socket");
+
 	/* Create sockets for them to listen to. */
 	atexit(destroy_fds);
 	sock = socket(PF_UNIX, SOCK_STREAM, 0);