Fix "Error displaying the error page: Application Instantiation Error" Error

This tries to "mask" a long standing bad behavior of the Joomla! CMS when a database connection can not be established.
The root cause are some bad designed exception handlers and wrong return values.
The effect is the following unhelpful message on a blank screen:

`Error displaying the error page: Application Instantiation Error`

The solution here is a very simple "fix" that only adds the **first** exception message to the final error output:

**Example:**

`Error displaying the error page: Application Instantiation Error: Could not connect to MySQL.`

So, at least one might have a clue what's going on :wink: 

**Test instructions:**
Change the database credentials in configuration.php to something invalid and reload the page.