tools/xenstored: fix possible NULL deref

Avoid dereferencing NULL in introduce_domain() when called during
live update.

Coverity ID: 1665111
Fixes: f78895ad78 ("tools/xenstored: Read event channel from xenstored page")
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>

tools/xenstored/domain.c

@@ -1032,7 +1032,7 @@ static struct domain *introduce_domain(const void *ctx,
 		if (!interface && !restore)
 			return NULL;
 
-		if (interface->evtchn_port)
+		if (!restore && interface->evtchn_port)
 			port = interface->evtchn_port;
 
 		if (new_domain(domain, port, restore)) {