xenstored: fix faulty check for bad handle in domain_init

Coverity-ID: 1054975
Coverity-ID: 1055196
Signed-off-by: Matthew Daley <mattjd@gmail.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/xenstore/xenstored_domain.c

@@ -640,7 +640,7 @@ void domain_init(void)
 		barf_perror("Failed to allocate domain gnttab handle");
 
 	*xcg_handle = xc_gnttab_open(NULL, 0);
-	if (*xcg_handle < 0)
+	if (*xcg_handle == NULL)
 		xprintf("WARNING: Failed to open connection to gnttab\n");
 	else
 		talloc_set_destructor(xcg_handle, close_xcg_handle);