Threadpool for scanning gets stuck in case one of the url is incorrect

[HenningL]

Given a list of urls to scan with a threadpoolexecutor and one of the url is incorrect:

`Caused by: org.reflections.ReflectionsException: could not create Vfs.Dir from url, no matching UrlType was found [file: .../$%7Bmaven.dependency.classpath%7D]
either use fromURL(final URL url, final List urlTypes) or use the static setDefaultURLTypes(final List urlTypes) or addDefaultURLTypes(UrlType urlType) with your specialized UrlType.
at org.reflections.vfs.Vfs.fromURL (Vfs.java:109)
at org.reflections.vfs.Vfs.fromURL (Vfs.java:91)
at org.reflections.Reflections.scan (Reflections.java:240)
at org.reflections.Reflections$1.run (Reflections.java:198)
at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:515)

The threadpool seems to not get destroyed and the execution gets stuck instead of either ignoring or finishing with error.