apps: use app_malloc_array()

apps: use app_malloc_array()

Replace app_malloc() calls where app_malloc_array() ones where
appropriate.

Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28444)