Allow usage of pointers to generic type in Scan method for sql.Null* …

[timsolov]

type Request struct {
    Name      *string // <--- not copying properly
    Num       int // <--- not copying properly
    CreatedAt *time.Time // <--- not copying properly
    UpdatedAt sql.NullTime
}

type Model struct {
    Name      sql.NullString
    Num       sql.NullInt32
    CreatedAt sql.NullTime
    UpdatedAt sql.NullTime
}

These fields don't copies. One new line resolve this issue.