Request for integrating #235774 - AssertionError: LibraryFiles{, packageInfo=nullversions={1.2=[base.css, base.min.css, layout.css, skeleton.css, skeleton.min.css]}}

Bug link:
https://netbeans.org/bugzilla/show_bug.cgi?id=235774

Description of the bug:
NetBeans can update bundled list of JavaScript libraries. Unfortunately,
the content of the ZIP archive we use does not have any format specified
so we must be very defensive. This fix improves the current behaviour.

Impact assessment:
This impacts all NetBeans users who try to update their JS libraries.

Risk assessment:
IMHO there is no risk since the assertions were simply replaced by a
proper check (and logging with FINE level).

Fix:
http://hg.netbeans.org/web-main/rev/796c63798a8c
http://hg.netbeans.org/web-main/rev/92e20090c008

The fix was written by tmysik, reviewed by dkonecny and verifed by vriha.

Thanks for the review,
Tomas