Move initial iterateVm checks to after step hook
Move initial iterateVm checks to after step hook

To ensure those conditions still generate a valid step for `runStepHook` handler.

ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-vm,ethereum/ethereumjs-vm,ethereumjs/ethereumjs-vm