apps/opt.c: next was only used when NDEBUG undefined, move it inside guard

Reviewed-by: Rich Salz <rsalz@openssl.org>

apps/opt.c

@@ -163,8 +163,8 @@ char *opt_init(int ac, char **av, const OPTIONS *o)
     unknown = NULL;
 
     for (; o->name; ++o) {
-        const OPTIONS *next;
 #ifndef NDEBUG
+        const OPTIONS *next;
         int duplicated, i;
 #endif