Import of relative dir in JAR is not working

When you try to import a dir relative to a group file which is loaded from a JAR, you get an NPE when closing the `InputStream` at `org.stringtemplate.v4.misc.Misc.urlExists(URL)`. This is a problem with the JDK, the same problem is described here: https://jira.springsource.org/browse/SPR-1629

My solution here is to put the close of the `InputStream` into a new finally block, swallowing all relevant  exceptions.