fix: reset Reader::SeekState when poll completed

[flisky]

I hereby agree to the terms of the CLA available at: https://databend.rs/dev/policies/cla/

Summary

a following seek will error with another search is in progress

[Xuanwo]

another search is in progress

Hi, the search here must be a typo, can you help fix it with seek?

[Xuanwo]

Let's merge first.