planner: fix prepare explain index out of range bug (#40568)#40602

Merged

ti-chi-bot merged 5 commits intopingcap:release-6.1from ti-chi-bot:cherry-pick-40568-to-release-6.1

Jan 17, 2023

+20-2

Commits on Jan 16, 2023

Commits on Jan 17, 2023