[Flang] Zero-sized FORALL is executed when the absolute values of both bounds are extremely large

This was discovered by @claude.

Consider the following code:

```fortran
program test_kind4all_1_2_v9
implicit none
integer(8), parameter :: sentinel = 99_8
integer(8), parameter :: lo = -HUGE(0_8)
integer(8), parameter :: hi = HUGE(0_8)
integer(8), dimension(2) :: A
A = sentinel
! stride=-1: zero-trip since lo < hi; (hi-lo-1)=-1 wraps on naive path to large positive
forall (integer(8) :: i = lo:hi:-1) A(1) = 0_8
if (A(1) /= sentinel) stop 1
if (A(2) /= sentinel) stop 2
print *, "pass"
end program
```

Since `lo` is less than `hi` and the step is negative, the set of combinations of *index-name* values should be empty.
However, Flang and GFortran seem to execute the *forall-assignment-stmt*: https://godbolt.org/z/sadrrGY7n

If the FORALL construct is replaced with a standard DO loop, GFortran behaves correctly, but Flang still fails.

Start with the provided Fortran reproducer and compare Flang's FORALL behavior with the standard DO-loop behavior described in the issue. Use the Godbolt example to reproduce the failure and inspect the Flang compiler path handling FORALL bounds and trip counts. Done means the zero-trip FORALL leaves both array elements unchanged and the reproducer prints "pass".

Written by the indexing model from the issue text.