[BUG] The tispark can't use index number of enum type column to select

[lilinghai]

Describe the bug

The tispark can't use index number of enum type column to select What did you do

1. execute in tidb create table t(c enum("good","bad") insert into t values("bad") insert into t values(null)
2. execute in tispark select * from t where c=2

What do you expect

'bad' What happens instead

empty Spark and TiSpark version info

Git Commit Hash: 9687b70202584883fe5b88d39fb62d64867ebde2 Git Branch: release-2.3 UTC Build Time: 2020-10-16 02:40:15 Supported Spark Version: 2.3 2.4 Current Spark Version: 2.4.3 Current Spark Major Version: 2.4 TimeZone: Asia/Shanghai

TIDB: release-4.0

[marsishandsome]

to fix

[shiyuhang0]

/lifecycle frozen