[MLIR][Affine] Fix getSliceBounds for missing handling of no lower/upper bound in certain cases (#127192)
Fix `FlatLinearValueConstraints::getSliceBounds` for missing checks on
no
lower/upper bound bound. Obvious bug.
Fixes: https://github.com/llvm/llvm-project/issues/119525
Fixes: https://github.com/llvm/llvm-project/issues/108374