Revert CI_DB_driver::_reset_select() to a regular method instead of abstract.abstract methods are required to be implemented by their child classes and this is not what's intended in our case.
diff --git a/system/database/DB_driver.php b/system/database/DB_driver.php
index 594fcce..45f17e8 100644
--- a/system/database/DB_driver.php
+++ b/system/database/DB_driver.php
@@ -1351,7 +1351,9 @@
*
* @return void
*/
- abstract protected function _reset_select();
+ protected function _reset_select()
+ {
+ }
}