[TYPO3-project-4-3] ExtJS: small issue when loading the default theme

[Fabien Udriot]

> thx, i committed the follow up.
> How did you found? Normally the t3skin-theme should be loaded.

I had a broken layout in my module. (BTW, it is funny to see an ExtJS application without CSS 
styles. The good News is that it is still usable...)

After investigation, I noticed that xtheme-*grey*.css was loaded whenever 
$GLOBALS['TBE_STYLES']['extJS']['theme'] is empty.

Fb.