Error handling of PDO driver broken

[Hackwar]

Steps to reproduce the issue

1. Edit your postgres install SQL and set the sequence ID of the assets table to something lower than the already used keys.
2. Install Joomla with Postgres (PDO)
3. Create a menu and save it.

Expected result

An error screen maybe with a stack trace and an error message that gives any hint what went wrong.

Actual result

You get a white screen with the text Recursion trying to check if connected.

System information (as much as possible)

Checkout from 4.0-dev

Additional comments

The issue seems to be with Joomla\Database\Pdo\PdoDriver::connected(). That method should check if the connection is alive and for that runs a query, which in turn calls execute(), which again calls connected() which then runs into the recursion condition.