[mlir][scf] Fix `for-loop-peeling` crash (#77697)

Before applying the peeling patterns, it can happen that the `ForOp`
gets a step of zero during folding. This leads to a division-by-zero
down the line.

This patch adds an additional check for a constant-zero step and a
 test.

Fix https://github.com/llvm/llvm-project/issues/75758