Restore module loading

The module loading feature got broken a while ago, so restore it, but
have it a bit more explicit this time around.

Reviewed-by: Stephen Henson <steve@openssl.org>
diff --git a/apps/s_server.c b/apps/s_server.c
index 6bbabcc..189019d 100644
--- a/apps/s_server.c
+++ b/apps/s_server.c
@@ -1438,6 +1438,9 @@
         goto end;
     }
 
+    if (!app_load_modules(NULL))
+        goto end;
+
     if (s_key_file == NULL)
         s_key_file = s_cert_file;