Installer fails if database name (new, not existing) contains dashes.

Steps to reproduce:

• run the installer.
• in "Database configuration", enter a new database name that contains dashes (e.g. drupal-test)

The installer shows a "Drupal already installed" error page on next step, and the installation is broken.

I have also noted that a database is created in that step (containing 20 tables) but does not contain the dashes (e.g. drupaltest).

This does not happen if the database already exists.