[flang][runtime] Fix IsContiguous for zero and one element arrays (#68869)

The byte strides in zero and one element array descriptor may not be
perfect multiple of the element size and previous and extents.

IsContiguous and its CFI equivalent should still return true for such
arrays (Fortran 2018 standards says in 8.5.7 that an array is not
contiguous if it has two or more elements and ....).