JavaCore#create() only returns null when the given project is null

The previous statements checked that, so just assert javaProject != null and remove
the null check.

This also helps Eclipse's null-pointer-access check.
Simplify the logic for #doLaunch()

If resource is null the method does nothing, but having the odd check inside the try makes
Eclipse complain about a potential null access in the catch. Just use an early return here.
Merge pull request #50 from ankon/fix-eclipse-null-checks

Fix eclipse null checks