only half of unicode string is inserted.

[huifly]

My Database is SQL Server 2019，collation is Chinese_PRC_CI_AI.
table test:
create table test (id int, name varchar(50), primary key (id))

code:
stmt, err := db.Prepare("insert into test(id, name) values(?,?)")
stmt.Exec(1, "张三")

result:
only "张" is inserted.

solution:
modify param.go line 71
case p.isDescribed:
sqltype = p.SQLType
// size should be column size.
if p.Size != 0 {
size = p.Size
}