Introjucer crash when adding image

Hi Jules, 

I'm trying to mess around with the resources in intro-jucer. Keep getting a crash with easy repro:

- Create new project

- Create new GUI component

- Add image to background

Crash at:

jucer_paintElementImage.g line 179:

                    jassertfalse; // this resource isn't valid!



Well, that's not a crash, it's an assertion.. And I can't reproduce it here!

I've been able to replicate this on both bleeding edge and v3.0.1. When an PaintElementImage is instantiated with an empty resource name, the assertion is triggered.

If you copy another image component it works fine.

FWIW I just commented out the assertion and all worked fine for me.

Yeah, it's not an important assertion, I'll remove it to avoid confusion.