Update LINDEX return value to better response

[hwware]

The problem/use-case that the feature addresses

Current LSET command:

LSET key index element: If key does not exist, return (error) ERR no such key
If key exists, but index out of range return (error) ERR index out of range
If key exists, but type not match, return (error) WRONGTYPE Operation against a key holding the wrong kind of value

We should make the LINDEX has the same return value:

LINDEX key index:

current return value:
If key does not exist, return nil
If key exists, but index out of range, return nil
If key exists, but type not match, return (error) WRONGTYPE Operation against a key holding the wrong kind of value