to resolve the ISSUE: #3139
When user execute query by some client library such as python MysqlDb, if user execute like:
"select * from tbl1;" (with a comma at the end of statement)
The sql parser will produce 2 statements: `SelectStmt` and `EmptyStmt`.
Here we discard the `EmptyStmt` to make it act like one single statement.
This is for some compatibility. Because in python MysqlDb, if the first `SelectStmt` results in
some warnings, it will try to execute a `SHOW WARNINGS` statement right after the
SelectStmt, but before the execution of `EmptyStmt`. So there will be an exception:
`(2014, "Commands out of sync; you can't run this command now")`
I though it is a flaw of python MysqlDb.
However, in order to maintain the consistency of user use, here we remove all EmptyStmt
at the end to prevent errors.(Leave at least one statement)
But if user execute statements like:
`"select * from tbl1;;select 2"`
If first `select * from tbl1` has warnings, python MysqlDb will still throw exception.
473a67a5b8