Fix bug that scripts may not be loaded correctly in pipeline

[canyousayyes]

Hello, I want to report a bug in the pipeline.ts and submit the bug fix as well.

---

Description

In the script checking part:

return this.redis
  .script('exists', Array.from(new Set(scripts.map(({ sha }) => sha))))
  .then(function (results) {
    var pending = [];
    for (var i = 0; i < results.length; ++i) {
      if (!results[i]) {
        pending.push(scripts[i]);
      }
    }

It will pass a uniqued scripts array (Array.from(new Set(scripts.map(({ sha }) => sha)))) into SCRIPT EXISTS, this is fine.
However it will add the scripts from the original scripts array (pending.push(scripts[i])), this could introduce a problem.

The bug seems to be introduced since #781.

---

Example

If I defined 2 custom commands echo and test, and do:

redis.pipeline()
  .echo()
  .echo()
  .test()

Then the scripts will contain ["echo", "echo", "test"], but the uniqued scripts array is ["echo", "test"].
The inconsistencies between the two arrays will make echo script will be loaded twice but test script not loading into Redis.

---

Fix

Please review my PR for the fix. I have moved the uniqueness check when adding the scripts.
Now there's only one scripts array and there should be no more inconsistency issue.

I have also updated the unit test to cover this case.

[luin]

Good catch! Thanks for your contribution!

[ioredis-robot]

🎉 This PR is included in version 4.16.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[canyousayyes]

Thanks for your swift response, I just need this new release for my app :)