egit/jgit: Upate Index (refresh) causes NullPointerException for "external" projects

Hi,

I think I found a bug in egit/jgit and can pin it down to "external"
projects, i.e., projects which reside in different directories than the
default workspace location.

Steps to reproduce:
 1. In Eclipse create a new project "foo" in an external location
(outside the default workspace location), say ~/bar/
 2. execute "git init" in that dir
 3. share project with git
 4. do a "Update Index (refresh)" operation and you'll get something
similar to

Counted 168 items to update in 0.0s

java.lang.NullPointerException
	at org.spearce.egit.core.internal.UpdateJob.run(UpdateJob.java:91)
	at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

All other git operations will also fail. However it will work if you
create project which is created in the default workspace and which
content is simply symlinked.

/HeX