[SPARK-22591][SQL] GenerateOrdering shouldn't change CodegenContext.INPUT_ROW

## What changes were proposed in this pull request?

When I played with codegen in developing another PR, I found the value of `CodegenContext.INPUT_ROW` is not reliable. Under wholestage codegen, it is assigned to null first and then suddenly changed to `i`.

The reason is `GenerateOrdering` changes `CodegenContext.INPUT_ROW` but doesn't restore it back.

## How was this patch tested?

Added test.

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #19800 from viirya/SPARK-22591.