DesignElement: Handling to avoid access to encrypted password from script should not cause "RuntimeException"

[speckyspooky]

With change #575 the option to get the encrypted "oda password" from script side was stopped.
This is a kind of security mechanism. Here are involved all parameters which has a binding to a data set to get the data dynamically.

If there is a try to fetch the oda password an RuntimeExcption will be throuwn to avoid the fetch.
The problem is here that the scripthandling will be brooken see #1617 where is given a very good case description
and with usage of the methode "getSelectionList()" the excpetion can be produced.

This change has also an impact for other specialized external PlugIns for BIRT which use the parameter task to get information from the parameters. Such special PlugIns will be detected also as scripted processing.

The solution here is to avoid that the RuntimeException will be thrown.
Instead of that it would be enough to return "null" of it. With this way the password is unpublished to the script context and the script can run anyway.

I will provide a PR for it.