Fixes switching between Scala Installations

It was a typo is a match case, introduced during the API refactoring
Fixed NPE on first start on Luna

In Luna preference initializers are called asynchronously outside of the UI thread.
The code used to get the current window was not working when not run on the UI thread.
The code from SWTUtils has a nice fallback.

Fixes #1002242
Merge pull request #782 from skyluc/issue/npe-key-binding-migration

Fixed NPE on first start on Luna
Merge pull request #781 from skyluc/issue/match-error-installations

Fixes switching between Scala Installations