tables: fix prefix index, when the charset is utf8, truncate it from runes (#7109)#7126

Merged

shenli merged 1 commit intopingcap:release-2.0from winkyao:cherry-pick-2.0

Jul 23, 2018

+48-12

Commits on Jul 23, 2018

tables: fix prefix index, when the charset is utf8, truncate it from runes (#7109 )
winkyao
committed