normal/menu: Use safe math to avoid an integer overflow

normal/menu: Use safe math to avoid an integer overflow

The Coverity indicates that the variable current_entry might overflow.
To prevent this use safe math when adding GRUB_MENU_PAGE_SIZE to current_entry.

On the occasion fix limiting condition which was broken.

Fixes: CID 473853
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Gbp-Pq: Topic cve-2025-jan
Gbp-Pq: Name normal-menu-Use-safe-math-to-avoid-an-integer-overflow.patch