Improve ziplistRandomPairs code logic (#8851)
Improve ziplistRandomPairs code logic (#8851)

After sorting, each item in picks is sorted according
to its index.

In the original code logic, we traverse from the first
element of ziplist until `zipindex == picks[pickindex].index`.

We may be able to start directly in `picks[0].index`,
this will bring small performance improvement.

Signed-off-by: ZheNing Hu <8dae2f6d2728458ed1e78928fecf94413e164809@gmail.com>
JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis