During org.eclipse.jdt.ui.tests.packageview.ContentProviderTests3
error randomly appeared if the GC did not finalized zipFile in time.

The problem was that getArchiveValidity() didn't properly closed opened 
(valid) jar files that were open over 2 minutes.

Change-Id: I845fcebc86175f08305749aca86bfc7a98fd6170
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/184069
Tested-by: Andrey Loskutov <loskutov@gmx.de>
Reviewed-by: Andrey Loskutov <loskutov@gmx.de>