Use the custom converter also for pointers

statement.go

@@ -119,7 +119,7 @@ func (stmt *mysqlStmt) Query(args []driver.Value) (driver.Rows, error) {
 
 type converter struct{}
 
-func (converter) ConvertValue(v interface{}) (driver.Value, error) {
+func (c converter) ConvertValue(v interface{}) (driver.Value, error) {
 	if driver.IsValue(v) {
 		return v, nil
 	}
@@ -131,7 +131,7 @@ func (converter) ConvertValue(v interface{}) (driver.Value, error) {
 		if rv.IsNil() {
 			return nil, nil
 		}
-		return driver.DefaultParameterConverter.ConvertValue(rv.Elem().Interface())
+		return c.ConvertValue(rv.Elem().Interface())
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 		return rv.Int(), nil
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32: